字节跳动最常考的 64 道JS算法题
缘起
现在大厂面试中,算法题几乎为必考项,且近几年频现 LeetCode 真题,此篇为拿到字节、腾讯、京东 Offer 的笔者本人在准备面试过程中亲自刷过以及遇到过高频算法题。文章内容会分模块整理,对于笔者在面试过程中遇到的真题,会给予着重 【🔥】标出。
同时,可以毫不客气的说,如果你准备时间有限,又想追求算法题准备效率最大化,那么你只需要按照大纲把下面的题目刷完,并把代码烂熟于心,就几乎可以应对 90% 的面试算法考题了。
整理这篇内容的目的一个是笔者在之前准备面试时的一点积累,而它确实也帮助笔者在面试算法题中过关斩将,同时呢,也希望能够在金三银四给予拼搏的你,一点点帮助就好!💪
文末有福利 :)😈
本篇内容包括如下模块:
- 高频算法题系列:链表
- 【🔥】【有真题】高频算法题系列:字符串
- 【🔥】【有真题】高频算法题系列:数组问题
- 高频算法题系列:二叉树
- 【🔥】高频算法题系列:排序算法
- 【🔥】高频算法题系列:二分查找
- 【🔥】高频算法题系列:动态规划
- 高频算法题系列:BFS
- 【🔥】高频算法题系列:栈
- 【🔥】高频算法题系列:DFS
- 【🔥】高频算法题系列:回溯算法
其中标🔥的部分代表非常高频的考题,其中不乏笔者遇到的原题。其中对于每一类,首先会列出包含的考题,然后针对每一道考题会给出难度、考察知识点、是否是面试真题,在每道题详细介绍时,还会给出每道题的 LeetCode 链接,帮助读者理解题意,以及能够进行实际的测验,还可以观看其他人的答案,更好的帮助准备。
高频算法题系列:链表
笔者遇到的高频链表题主要包含这几道:
- 通过链表的后续遍历判断回文链表问题 【简单】
- 链表的反向输出 【简单】
- 合并 K 个升序链表 【困难】
- K个一组翻转链表 【困难】
- 环形链表 【简单】
- 排序链表 【中等】
- 相交链表 【简单】
前序遍历判断回文链表
题解1
利用链表的后续遍历,使用函数调用栈作为后序遍历栈,来判断是否回文
→点击展开查看
/**
*
*/
var isPalindrome = function(head) {
let left = head;
function traverse(right) {
if (right == null) return true;
let res = traverse(right.next);
res = res && (right.val === left.val);
left = left.next;
return res;
}
return traverse(head);
};
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题解2
通过 快、慢指针找链表中点,然后反转链表,比较两个链表两侧是否相等,来判断是否是回文链表
→点击展开查看
/**
*
*/
var isPalindrome = function(head) {
// 反转 slower 链表
let right = reverse(findCenter(head));
let left = head;
// 开始比较
while (right != null) {
if (left.val !== right.val) {
return false;
}
left = left.next;
right = right.next;
}
return true;
}
function findCenter(head) {
let slower = head, faster = head;
while (faster && faster.next != null) {
slower = slower.next;
faster = faster.next.next;
}
// 如果 faster 不等于 null,说明是奇数个,slower 再移动一格
if (faster != null) {
slower = slower.next;
}
return slower;
}
function reverse(head) {
let prev = null, cur = head, nxt = head;
while (cur != null) {
nxt = cur.next;
cur.next = prev;
prev = cur;
cur = nxt;
}
return prev;
}
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反转链表
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var reverseList = function(head) {
if (head == null || head.next == null) return head;
let last = reverseList(head.next);
head.next.next = head;
head.next = null;
return last;
};
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合并K个升序链表
👉 【LeetCode 直通车】:23 合并K个升序链表(困难)
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode[]} lists
* @return {ListNode}
*/
var mergeKLists = function(lists) {
if (lists.length === 0) return null;
return mergeArr(lists);
};
function mergeArr(lists) {
if (lists.length <= 1) return lists[0];
let index = Math.floor(lists.length / 2);
const left = mergeArr(lists.slice(0, index))
const right = mergeArr(lists.slice(index));
return merge(left, right);
}
function merge(l1, l2) {
if (l1 == null && l2 == null) return null;
if (l1 != null && l2 == null) return l1;
if (l1 == null && l2 != null) return l2;
let newHead = null, head = null;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
if (!head) {
newHead = l1;
head = l1;
} else {
newHead.next = l1;
newHead = newHead.next;
}
l1 = l1.next;
} else {
if (!head) {
newHead = l2;
head = l2;
} else {
newHead.next = l2;
newHead = newHead.next;
}
l2 = l2.next;
}
}
newHead.next = l1 ? l1 : l2;
return head;
}
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K 个一组翻转链表
👉 【LeetCode 直通车】:25 K 个一组翻转链表(困难)
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @param {number} k
* @return {ListNode}
*/
var reverseKGroup = function(head, k) {
let a = head, b = head;
for (let i = 0; i < k; i++) {
if (b == null) return head;
b = b.next;
}
const newHead = reverse(a, b);
a.next = reverseKGroup(b, k);
return newHead;
};
function reverse(a, b) {
let prev = null, cur = a, nxt = a;
while (cur != b) {
nxt = cur.next;
cur.next = prev;
prev = cur;
cur = nxt;
}
return prev;
}
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环形链表
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {boolean}
*/
var hasCycle = function(head) {
if (head == null || head.next == null) return false;
let slower = head, faster = head;
while (faster != null && faster.next != null) {
slower = slower.next;
faster = faster.next.next;
if (slower === faster) return true;
}
return false;
};
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排序链表
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var sortList = function(head) {
if (head == null) return null;
let newHead = head;
return mergeSort(head);
};
function mergeSort(head) {
if (head.next != null) {
let slower = getCenter(head);
let nxt = slower.next;
slower.next = null;
console.log(head, slower, nxt);
const left = mergeSort(head);
const right = mergeSort(nxt);
head = merge(left, right);
}
return head;
}
function merge(left, right) {
let newHead = null, head = null;
while (left != null && right != null) {
if (left.val < right.val) {
if (!head) {
newHead = left;
head = left;
} else {
newHead.next = left;
newHead = newHead.next;
}
left = left.next;
} else {
if (!head) {
newHead = right;
head = right;
} else {
newHead.next = right;
newHead = newHead.next;
}
right = right.next;
}
}
newHead.next = left ? left : right;
return head;
}
function getCenter(head) {
let slower = head, faster = head.next;
while (faster != null && faster.next != null) {
slower = slower.next;
faster = faster.next.next;
}
return slower;
}
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相交链表
题解
→点击展开查看
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} headA
* @param {ListNode} headB
* @return {ListNode}
*/
var getIntersectionNode = function(headA, headB) {
let lastHeadA = null;
let lastHeadB = null;
let originHeadA = headA;
let originHeadB = headB;
if (!headA || !headB) {
return null;
}
while (true) {
if (headB == headA) {
return headB;
}
if (headA && headA.next == null) {
lastHeadA = headA;
headA = originHeadB;
} else {
headA = headA.next;
}
if (headB && headB.next == null) {
lastHeadB = headB
headB = originHeadA;
} else {
headB = headB.next;
}
if (lastHeadA && lastHeadB && lastHeadA != lastHeadB) {
return null;
}
}
return null;
};
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【🔥】高频算法题系列:字符串
主要有以下几类高频考题:
- 最长回文子串 【中等】【双指针】【面试真题】
- 最长公共前缀 【简单】【双指针】
- 无重复字符的最长子串【中等】【双指针】
- 最小覆盖子串 【困难】【滑动窗口】【面试真题】
【面试真题】最长回文子串【双指针】
题解
→点击展开查看
/**
* @param {string} s
* @return {string}
*/
var longestPalindrome = function(s) {
if (s.length === 1) return s;
let maxRes = 0, maxStr = '';
for (let i = 0; i < s.length; i++) {
let str1 = palindrome(s, i, i);
let str2 = palindrome(s, i, i + 1);
if (str1.length > maxRes) {
maxStr = str1;
maxRes = str1.length;
}
if (str2.length > maxRes) {
maxStr = str2;
maxRes = str2.length;
}
}
return maxStr;
};
function palindrome(s, l, r) {
while (l >= 0 && r < s.length && s[l] === s[r]) {
l--;
r++;
}
return s.slice(l + 1, r);
}
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最长公共前缀【双指针】
👉 【LeetCode 直通车】:14 最长公共前缀(简单)
题解
→点击展开查看
/**
* @param {string[]} strs
* @return {string}
*/
var longestCommonPrefix = function(strs) {
if (strs.length === 0) return "";
let first = strs[0];
if (first === "") return "";
let minLen = Number.MAX_SAFE_INTEGER;
for (let i = 1; i < strs.length; i++) {
const len = twoStrLongestCommonPrefix(first, strs[i]);
minLen = Math.min(len, minLen);
}
return first.slice(0, minLen);
};
function twoStrLongestCommonPrefix (s, t) {
let i = 0, j = 0;
let cnt = 0;
while (i < s.length && j < t.length) {
console.log(s[i], t[j], cnt)
if (s[i] === t[j]) {
cnt++;
} else {
return cnt;
}
i++;
j++;
}
return cnt;
}
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无重复字符的最长子串【双指针】
👉 【LeetCode 直通车】:3 无重复字符的最长子串(中等)
题解
→点击展开查看
/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function(s) {
let window = {};
let left = 0, right = 0;
let maxLen = 0, maxStr = '';
while (right < s.length) {
let c = s[right];
right++;
if (window[c]) window[c]++;
else window[c] = 1
while (window[c] > 1) {
let d = s[left];
left++;
window[d]--;
}
if (maxLen < right - left) {
maxLen = right - left;
}
}
return maxLen;
};
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【面试真题】 最小覆盖子串【滑动窗口】
👉 【LeetCode 直通车】:76 最小覆盖子串(困难)
题解
→点击展开查看
/**
* @param {string} s
* @param {string} t
* @return {string}
*/
var minWindow = function(s, t) {
let need = {}, window = {};
for (let c of t) {
if (!need[c]) need[c] = 1;
else need[c]++;
}
let left = 0, right = 0;
let valid = 0, len = Object.keys(need).length;
let minLen = s.length + 1, minStr = '';
while (right < s.length) {
const d = s[right];
right++;
if (!window[d]) window[d] = 1;
else window[d]++;
if (need[d] && need[d] === window[d]) {
valid++;
}
console.log('left - right', left, right);
while (valid === len) {
if (right - left < minLen) {
minLen = right - left;
minStr = s.slice(left, right);
}
console.lo
let c = s[left];
left++;
window[c]--;
if (need[c] && window[c] < need[c]) {
valid--;
}
}
}
return minStr;
};
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【🔥】高频算法题系列:数组问题
主要有几类高频考题:
- 俄罗斯套娃信封问题【困难】【排序+最长上升子序列】【面试真题】
- 最长连续递增序列 【简单】【双指针】
- 最长连续序列【困难】【哈希表】
- 盛最多水的容器【困难】【面试真题】
- 寻找两个正序数组的中位数【困难】【双指针】
- 删除有序数组中的重复项【简单】【快慢指针】
- 和为K的子数组【中等】【哈希表】
- nSum 问题【系列】【简单】【哈希表】
- 接雨水【困难】【暴力+备忘录优化】【面试真题】
- 跳跃游戏【系列】【中等】【贪心算法】
【面试真题】俄罗斯套娃信封问题【排序+最长上升子序列】
👉 【LeetCode 直通车】:354 俄罗斯套娃信封问题(困难)
题解
→点击展开查看
/**
* @param {number[][]} envelopes
* @return {number}
*/
var maxEnvelopes = function(envelopes) {
if (envelopes.length === 1) return 1;
envelopes.sort((a, b) => {
if (a[0] !== b[0]) return a[0] - b[0];
else return b[1] - a[1];
});
let LISArr = [];
for (let [key, value] of envelopes) {
LISArr.push(value);
}
console.log( LISArr);
return LIS(LISArr);
};
function LIS(arr) {
let dp = [];
let maxAns = 0;
for (let i = 0; i < arr.length; i++) {
dp[i] = 1;
}
for (let i = 1; i < arr.length; i++) {
for (let j = i; j >= 0; j--) {
if (arr[i] > arr[j]) {
dp[i] = Math.max(dp[i], dp[j] + 1)
}
maxAns = Math.max(maxAns, dp[i]);
}
}
return maxAns;
}
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最长连续递增序列【快慢指针】
👉 【LeetCode 直通车】:674 最长连续递增序列(简单)
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number}
*/
var findLengthOfLCIS = function(nums) {
if (nums.length === 0) return 0;
const n = nums.length;
let left = 0, right = 1;
let globalMaxLen = 1, maxLen = 1;
while (right < n) {
if (nums[right] > nums[left]) maxLen++;
else {
maxLen = 1;
}
left++;
right++;
globalMaxLen = Math.max(globalMaxLen, maxLen);
}
return globalMaxLen;
};
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最长连续序列 【哈希表】
👉 【LeetCode 直通车】:128 最长连续序列(困难)
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number}
*/
var longestConsecutive = function(nums) {
if (nums.length === 0) return 0;
const set = new Set(nums);
const n = nums.length;
let globalLongest = 1;
for (let i = 0; i < n; i++) {
if (!set.has(nums[i] - 1)) {
let longest = 1;
let currentNum = nums[i];
while (set.has(currentNum + 1)) {
currentNum += 1;
longest++;
}
globalLongest = Math.max(globalLongest, longest);
}
}
return globalLongest;
};
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【面试真题】盛最多水的容器【哈希表】
👉 【LeetCode 直通车】:11 盛最多水的容器(中等)
题解
→点击展开查看
/**
* @param {number[]} height
* @return {number}
*/
var maxArea = function(height) {
let n = height.length;
let left = 0, right = n - 1;
let maxOpacity = 0;
while (left < right) {
let res = Math.min(height[left], height[right]) * (right - left);
maxOpacity = Math.max(maxOpacity, res);
if (height[left] < height[right]) left++
else right--;
}
return maxOpacity;
};
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寻找两个正序数组的中位数【双指针】
👉 【LeetCode 直通车】:4 寻找两个正序数组的中位数(困难)
题解
→点击展开查看
/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number}
*/
var findMedianSortedArrays = function(nums1, nums2) {
let m = nums1.length, n = nums2.length;
let i = 0, j = 0;
let newArr = [];
while (i < m && j < n) {
if (nums1[i] < nums2[j]) {
newArr.push(nums1[i++]);
} else {
newArr.push(nums2[j++]);
}
}
newArr = newArr.concat(i < m ? nums1.slice(i) : nums2.slice(j));
const len = newArr.length;
console.log(newArr)
if (len % 2 === 0) {
return (newArr[len / 2] + newArr[len / 2 - 1]) / 2;
} else {
return newArr[Math.floor(len / 2)];
}
};
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删除有序数组中的重复项【快慢指针】
👉 【LeetCode 直通车】:26 删除有序数组中的重复项(简单)
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number}
*/
var removeDuplicates = function(nums) {
if (nums.length <= 1) return nums.length;
let lo = 0, hi = 0;
while (hi < nums.length) {
while (nums[lo] === nums[hi] && hi < nums.length) hi++;
if (nums[lo] !== nums[hi] && hi < nums.length) {
lo++;
nums[lo] = nums[hi];
}
hi++;
}
return lo + 1;
};
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和为K的子数组【哈希表】
👉 【LeetCode 直通车】:560 和为K的子数组(中等)
题解
→点击展开查看
/**
* @param {number[]} nums
* @param {number} k
* @return {number}
*/
var subarraySum = function(nums, k) {
let cnt = 0;
let sum0_i = 0, sum0_j = 0;
let map = new Map();
map.set(0, 1);
for (let i = 0; i <= nums.length; i++) {
sum0_i += nums[i];
sum0_j = sum0_i - k;
console.log('map', sum0_j, map.get(sum0_j))
if (map.has(sum0_j)) {
cnt += map.get(sum0_j);
}
let sumCnt = map.get(sum0_i) || 0;
map.set(sum0_i, sumCnt + 1);
}
return cnt;
};
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nSum问题【哈希表】【系列】
- 👉 【LeetCode 直通车】:1 两数之和(简单)
- 👉 【LeetCode 直通车】:167 两数之和 II - 输入有序数组(简单)
- 👉 【LeetCode 直通车】:15 三数之和(中等)
- 👉 【LeetCode 直通车】:18 四数之和(中等)
受限于篇幅,这里只给出第一道题的代码模板,也是一面常考真题。
题解
→点击展开查看
/**
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var twoSum = function(nums, target) {
let map2 = new Map();
for (let i = 0; i < nums.length; i++) {
map2.set(nums[i], i);
}
for (let i = 0; i < nums.length; i++) {
if (map2.has(target - nums[i]) && map2.get(target - nums[i]) !== i) return [i, map2.get(target - nums[i])]
}
};
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【面试真题】接雨水【暴力+备忘录优化】
题解
→点击展开查看
/**
* @param {number[]} height
* @return {number}
*/
var trap = function(height) {
let l_max = [], r_max = [];
let len = height.length;
let maxCapacity = 0;
for (let i = 0; i < len; i++) {
l_max[i] = height[i];
r_max[i] = height[i];
}
for (let i = 1; i < len; i++) {
l_max[i] = Math.max(l_max[i - 1], height[i]);
}
for (let j = len - 2; j >= 0; j--) {
r_max[j] = Math.max(r_max[j + 1], height[j]);
}
for (let i = 0; i < len; i++) {
maxCapacity += Math.min(l_max[i], r_max[i]) - height[i];
}
return maxCapacity;
};
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跳跃游戏【贪心算法】【系列】
受限于篇幅,这里只给出第一道题的代码模板,也是一面常考真题。
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {boolean}
*/
var canJump = function(nums) {
let faster = 0;
for (let i = 0; i < nums.length - 1; i++) {
faster = Math.max(faster, i + nums[i]);
if (faster <= i) return false;
}
return faster >= nums.length - 1;
};
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高频算法题系列:二叉树
主要有以下几类高频考题:
- 二叉树的最近公共祖先【简单】【二叉树】
- 二叉搜索树中的搜索【简单】【二叉树】
- 删除二叉搜索树中的节点【中等】【二叉树】
- 完全二叉树的节点个数【中等】【二叉树】
- 二叉树的锯齿形层序遍历【中等】【二叉树】
二叉树的最近公共祖先【二叉树】
👉 【LeetCode 直通车】:236 二叉树的最近公共祖先(简单)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {TreeNode} p
* @param {TreeNode} q
* @return {TreeNode}
*/
let visited;let parent;
var lowestCommonAncestor = function(root, p, q) {
visited = new Set();
parent = new Map();
dfs(root);
while (p != null) {
visited.add(p.val);
p = parent.get(p.val);
}
while (q != null) {
if (visited.has(q.val)) {
return q;
}
q = parent.get(q.val);
}
return null;
};
function dfs(root) {
if (root.left != null) {
parent.set(root.left.val, root);
dfs(root.left);
}
if (root.right != null) {
parent.set(root.right.val, root);
dfs(root.right);
}
}
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二叉搜索树中的搜索【二叉树】
👉 【LeetCode 直通车】:700 二叉搜索树中的搜索(简单)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {number} val
* @return {TreeNode}
*/
var searchBST = function(root, val) {
if (root == null) return null;
if (root.val === val) return root;
if (root.val > val) {
return searchBST(root.left, val);
} else if (root.val < val) {
return searchBST(root.right, val);
}
};
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删除二叉搜索树中的节点【二叉树】
👉 【LeetCode 直通车】:450 删除二叉搜索树中的节点(中等)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {number} key
* @return {TreeNode}
*/
var deleteNode = function(root, key) {
if (root == null) return null;
if (root.val === key) {
if (root.left == null && root.right == null) return null;
if (root.left == null) return root.right;
if (root.right == null) return root.left;
if (root.left != null && root.right != null) {
let target = getMinTreeMaxNode(root.left);
root.val = target.val;
root.left = deleteNode(root.left, target.val);
}
}
if (root.val < key) {
root.right = deleteNode(root.right, key);
} else if (root.val > key) {
root.left = deleteNode(root.left, key);
}
return root;
};
function getMinTreeMaxNode(root) {
if (root.right == null) return root;
return getMinTreeMaxNode(root.right);
}
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完全二叉树的节点个数【二叉树】
👉 【LeetCode 直通车】:222 完全二叉树的节点个数(中等)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var countNodes = function(root) {
if (root == null) return 0;
let l = root, r = root;
let lh = 0, rh = 0;
while (l != null) {
l = l.left;
lh++;
}
while (r != null) {
r = r.right;
rh++;
}
if (lh === rh) {
return Math.pow(2, lh) - 1;
}
return 1 + countNodes(root.left) + countNodes(root.right);
};
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二叉树的锯齿形层序遍历【二叉树】
👉 【LeetCode 直通车】:103 二叉树的锯齿形层序遍历(中等)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[][]}
*/
let res;
var zigzagLevelOrder = function(root) {
if (root == null) return [];
res = [];
BFS(root, true);
return res;
};
function BFS(root, inOrder) {
let arr = [];
let resItem = [];
let node;
let stack1 = new Stack();
let stack2 = new Stack();
// 判断交换时机
let flag;
stack1.push(root);
res.push([root.val]);
inOrder = !inOrder;
while (!stack1.isEmpty() || !stack2.isEmpty()) {
if (stack1.isEmpty()) {
flag = 'stack1';
} else if (stack2.isEmpty()) {
flag = 'stack2';
}
// 决定取那个栈里面的元素
if (flag === 'stack2' && !stack1.isEmpty()) node = stack1.pop();
else if (flag === 'stack1' && !stack2.isEmpty()) node = stack2.pop();
if (inOrder) {
if (node.left) {
if (flag === 'stack1') {
stack1.push(node.left);
} else {
stack2.push(node.left);
}
resItem.push(node.left.val);
}
if (node.right) {
if (flag === 'stack1') {
stack1.push(node.right);
} else {
stack2.push(node.right);
}
resItem.push(node.right.val);
}
} else {
if (node.right) {
if (flag === 'stack1') {
stack1.push(node.right);
} else {
stack2.push(node.right);
}
resItem.push(node.right.val);
}
if (node.left) {
if (flag === 'stack1') {
stack1.push(node.left);
} else {
stack2.push(node.left);
}
resItem.push(node.left.val);
}
}
// 判断下次翻转的时机
if ((flag === 'stack2' && stack1.isEmpty()) || (flag === 'stack1' && stack2.isEmpty())) {
inOrder = !inOrder;
// 需要翻转了,就加一轮值
if (resItem.length > 0) {
res.push(resItem);
}
resItem = [];
}
}
}
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return undefined;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
size() {
return this.count;
}
isEmpty() {
return this.size() === 0;
}
}
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【🔥】高频算法题系列:排序算法
主要有以下几类高频考题:
- 用最少数量的箭引爆气球【中等】【排序】
- 合并区间【中等】【排序算法+区间问题】【面试真题】
用最少数量的箭引爆气球【排序算法】
👉 【LeetCode 直通车】:452 用最少数量的箭引爆气球(中等)
题解
→点击展开查看
/**
* @param {number[][]} points
* @return {number}
*/
var findMinArrowShots = function(points) {
if (points.length === 0) return 0;
points.sort((a, b) => a[1] - b[1]);
let cnt = 1;
let resArr = [points[0]];
let curr, last;
for (let i = 1; i < points.length; i++) {
curr = points[i];
last = resArr[resArr.length - 1];
if (curr[0] > last[1]) {
resArr.push(curr);
cnt++;
}
}
return cnt;
};
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合并区间【排序算法+区间问题】
题解
→点击展开查看
/**
* @param {number[][]} intervals
* @return {number[][]}
*/
var merge = function(intervals) {
if (intervals.length === 0) return [];
intervals.sort((a, b) => a[0] - b[0]);
let mergeArr = [intervals[0]];
let last, curr;
for (let j = 1; j < intervals.length; j++) {
last = mergeArr[mergeArr.length - 1];
curr = intervals[j];
if (last[1] >= curr[0]) {
last[1] = Math.max(curr[1], last[1]);
} else {
mergeArr.push(curr);
}
}
return mergeArr;
};
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高频算法题系列:二分查找
主要有以下几类高频考题:
- 寻找两个正序数组的中位数【困难】【二分查找】
- 判断子序列【简单】【二分查找】
- 在排序数组中查找元素的第一个和最后一个位置【中等】【二分查找】
寻找两个正序数组的中位数【二分查找】
👉 【LeetCode 直通车】:4 寻找两个正序数组的中位数(困难)
题解
→点击展开查看
/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number}
*/
var findMedianSortedArrays = function(nums1, nums2) {
let m = nums1.length, n = nums2.length;
let i = 0, j = 0;
let newArr = [];
while (i < m && j < n) {
if (nums1[i] < nums2[j]) {
newArr.push(nums1[i++]);
} else {
newArr.push(nums2[j++]);
}
}
newArr = newArr.concat(i < m ? nums1.slice(i) : nums2.slice(j));
const len = newArr.length;
console.log(newArr)
if (len % 2 === 0) {
return (newArr[len / 2] + newArr[len / 2 - 1]) / 2;
} else {
return newArr[Math.floor(len / 2)];
}
};
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判断子序列【二分查找】
👉 【LeetCode 直通车】:392 判断子序列(简单)
题解
→点击展开查看
/**
* @param {string} s
* @param {string} t
* @return {boolean}
*/
var isSubsequence = function(s, t) {
let hash = {};
for (let i = 0; i < t.length; i++) {
if (!hash[t[i]]) hash[t[i]] = [];
hash[t[i]].push(i);
}
let lastMaxIndex = 0;
for (let i = 0; i < s.length; i++) {
if (hash[s[i]]) {
const index = binarySearch(hash[s[i]], lastMaxIndex);
console.log('index', index, hash[s[i]]);
if (index === -1) return false;
lastMaxIndex = hash[s[i]][index] + 1;
} else return false;
}
return true;
};
function binarySearch(array, targetIndex) {
let left = 0, right = array.length;
while (left < right) {
let mid = left + Math.floor((right - left) / 2);
if (array[mid] >= targetIndex) {
right = mid;
} else if (array[mid] < targetIndex) {
left = mid + 1;
}
}
if (left >= array.length || array[left] < targetIndex) return -1;
return left;
}
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💁 在排序数组中查找元素的第一个和最后一个位置【二分搜索】
👉 【LeetCode 直通车】:34 在排序数组中查找元素的第一个和最后一个位置(中等)
题解
→点击展开查看
/**
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var searchRange = function(nums, target) {
const left = leftBound(nums, target);
const right = rightBound(nums, target);
return [left, right];
};
function leftBound(nums, target) {
let left = 0;
let right = nums.length - 1;
while (left <= right) {
let mid = Math.floor(left + (right - left) / 2);
if (nums[mid] === target) {
right = mid - 1;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid - 1;
}
}
if (left >= nums.length || nums[left] !== target) {
return -1;
}
return left;
}
function rightBound(nums, target) {
let left = 0;
let right = nums.length - 1;
while (left <= right) {
let mid = Math.floor(left + (right - left) / 2);
if (nums[mid] === target) {
left = mid + 1;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid - 1;
}
}
if (right < 0 || nums[right] !== target) {
return -1;
}
return right;
}
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【🔥】高频算法题系列:动态规划
主要有以下几类高频考题:
- 最长递增子序列【中等】【动态规划】
- 零钱兑换【中等】【动态规划】【面试真题】
- 最长公共子序列 【中等】【动态规划】【面试真题】
- 编辑距离 【困难】【动态规划】
- 最长回文子序列【中等】【动态规划】【面试真题】
- 最大子序和【简单】【动态规划】【面试真题】
- 买卖股票的最佳时机系列【系列】【动态规划】【面试真题】
最长递增子序列【动态规划】
👉 【LeetCode 直通车】:300 最长递增子序列(中等)
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number}
*/
var lengthOfLIS = function(nums) {
let maxLen = 0, n = nums.length;
let dp = [];
for (let i = 0; i < n; i++) {
dp[i] = 1;
}
for (let i = 0; i < n; i++) {
for (let j = 0; j < i; j++) {
if (nums[i] > nums[j]) {
dp[i] = Math.max(dp[i], dp[j] + 1);
}
}
maxLen = Math.max(maxLen, dp[i]);
}
return maxLen;
};
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【面试真题】 零钱兑换【动态规划】
题解
→点击展开查看
/**
* @param {number[]} coins
* @param {number} amount
* @return {number}
*/
var coinChange = function(coins, amount) {
if (amount === 0) return 0;
let dp = [];
for (let i = 0; i <= amount; i++) {
dp[i] = amount + 1;
}
dp[0] = 0;
for (let i = 0; i <= amount; i++) {
for (let j = 0; j < coins.length; j++) {
if (i >= coins[j]) {
dp[i] = Math.min(dp[i - coins[j]] + 1, dp[i])
}
}
}
return dp[amount] === amount + 1 ? -1 : dp[amount];
};
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【面试真题】 最长公共子序列【动态规划】
👉 【LeetCode 直通车】:1143 最长公共子序列(中等)
题解
→点击展开查看
/**
* @param {string} text1
* @param {string} text2
* @return {number}
*/
var longestCommonSubsequence = function(text1, text2) {
let n1 = text1.length, n2 = text2.length;
let dp = [];
for (let i = -1; i < n1; i++) {
dp[i] = [];
for (let j = -1; j < n2;j++) {
dp[i][j] = 0;
}
}
for (let i = 0; i < n1; i++) {
for (let j = 0; j < n2; j++) {
if (text1[i] === text2[j]) {
dp[i][j] = Math.max(dp[i][j], dp[i - 1][j - 1] + 1);
} else {
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1])
}
}
}
return dp[n1 - 1][n2 - 1];
};
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编辑距离【动态规划】
题解
→点击展开查看
/**
* @param {string} word1
* @param {string} word2
* @return {number}
*/
var minDistance = function(word1, word2) {
let len1 = word1.length, len2 = word2.length;
let dp = [];
for (let i = 0; i <= len1; i++) {
dp[i] = [];
for (let j = 0; j <= len2; j++) {
dp[i][j] = 0;
if (i === 0) {
dp[i][j] = j;
}
if (j === 0) {
dp[i][j] = i;
}
}
}
for (let i = 1; i <= len1; i++) {
for (let j = 1; j <= len2; j++) {
if (word1[i - 1] === word2[j - 1]) {
dp[i][j] = dp[i - 1][j - 1];
} else {
dp[i][j] = Math.min(dp[i - 1][j] + 1, dp[i][j - 1] + 1, dp[i - 1][j - 1] + 1);
}
}
}
return dp[len1][len2];
};
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【面试真题】最长回文子序列【动态规划】
👉 【LeetCode 直通车】:516 最长回文子序列(中等)
题解
→点击展开查看
/**
* @param {string} s
* @return {number}
*/
var longestPalindromeSubseq = function(s) {
let dp = [];
for (let i = 0; i < s.length; i++) {
dp[i] = [];
for (let j = 0; j < s.length; j++) {
dp[i][j] = 0;
}
dp[i][i] = 1;
}
for (let i = s.length - 1; i >= 0; i--) {
for (let j = i + 1; j < s.length; j++) {
if (s[i] === s[j]) {
dp[i][j] = dp[i + 1][j - 1] + 2;
} else {
dp[i][j] = Math.max(dp[i + 1][j], dp[i][j - 1]);
}
}
}
return dp[0][s.length - 1];
};
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【面试真题】💁 最大子序和【动态规划】
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number}
*/
var maxSubArray = function(nums) {
let maxSum = -Infinity;
let dp = [], n = nums.length;
for (let i = -1; i < n; i++) {
dp[i] = 0;
}
for (let i = 0; i < n; i++) {
dp[i] = Math.max(nums[i], dp[i - 1] + nums[i]);
maxSum = Math.max(maxSum, dp[i]);
}
return maxSum;
};
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【面试真题】💁 买卖股票的最佳时机【动态规划】
- 👉 【LeetCode 直通车】:121 买卖股票的最佳时机(简单)【面试真题】
- 👉 【LeetCode 直通车】:122 买卖股票的最佳时机 II(简单)
- 👉 【LeetCode 直通车】:123 买卖股票的最佳时机 III(困难)
- 👉 【LeetCode 直通车】:188 买卖股票的最佳时机IV(困难)
- 👉 【LeetCode 直通车】:309 买卖股票的最佳时机含冷冻期(中等)
- 👉 【LeetCode 直通车】:714 买卖股票的最佳时机含手续费(中等)
受限于篇幅,这里只给出第一道题的代码模板,也是一面常考真题,笔者在面试字节跳动时就遇到过。
题解
→点击展开查看
/**
* @param {number[]} prices
* @return {number}
*/
var maxProfit = function(prices) {
let dp = [];
for (let i = -1; i < prices.length; i++) {
dp[i] = []
for (let j = 0; j <= 1; j++) {
dp[i][j] = [];
dp[i][j][0] = 0;
dp[i][j][1] = 0;
if (i === -1) {
dp[i][j][1] = -Infinity;
}
if (j === 0) {
dp[i][j][1] = -Infinity;
}
if (j === -1) {
dp[i][j][1] = -Infinity;
}
}
}
for (let i = 0; i < prices.length; i++) {
for (let j = 1; j <= 1; j++) {
dp[i][j][0] = Math.max(dp[i - 1][j][0], dp[i - 1][j][1] + prices[i]);
dp[i][j][1] = Math.max(dp[i - 1][j][1], dp[i - 1][j - 1][0] - prices[i]);
}
}
return dp[prices.length - 1][1][0];
};
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高频算法题系列:BFS
主要有以下几类高频考题:
- 打开转盘锁【中等】【BFS】
- 二叉树的最小深度【简单】【BFS】
打开转盘锁【BFS】
👉 【LeetCode 直通车】:752 打开转盘锁(中等)
题解
→点击展开查看
/**
* @param {string[]} deadends
* @param {string} target
* @return {number}
*/
var openLock = function(deadends, target) {
let queue = new Queue();
let visited = new Set();
let step = 0;
queue.push('0000');
visited.add('0000');
while (!queue.isEmpty()) {
let size = queue.size();
for (let i = 0; i < size; i++) {
let str = queue.pop();
if (deadends.includes(str)) continue;
if (target === str) {
return step;
}
for (let j = 0; j < 4; j++) {
let plusStr = plusOne(str, j);
let minusStr = minusOne(str, j);
if (!visited.has(plusStr)) {
queue.push(plusStr);
visited.add(plusStr)
}
if (!visited.has(minusStr)) {
queue.push(minusStr);
visited.add(minusStr)
}
}
}
step++;
}
return -1;
};
function plusOne(str, index) {
let strArr = str.split('');
if (strArr[index] === '9') {
strArr[index] = '0'
} else {
strArr[index] = (Number(strArr[index]) + 1).toString()
}
return strArr.join('');
}
function minusOne(str, index) {
let strArr = str.split('');
if (strArr[index] === '0') {
strArr[index] = '9'
} else {
strArr[index] = (Number(strArr[index]) - 1).toString()
}
return strArr.join('');
}
class Queue {
constructor() {
this.items = [];
this.count = 0;
this.lowerCount = 0;
}
push(elem) {
this.items[this.count++] = elem;
}
pop() {
if (this.isEmpty()) {
return;
}
const elem = this.items[this.lowerCount];
delete this.items[this.lowerCount];
this.lowerCount++;
return elem;
}
isEmpty() {
if (this.size() === 0) return true;
return false;
}
size() {
return this.count - this.lowerCount;
}
}
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二叉树的最小深度【BFS】
👉 【LeetCode 直通车】:111 二叉树的最小深度(简单)
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var minDepth = function(root) {
if (root == null) return 0;
let depth = 1;
let queue = new Queue();
queue.push(root);
while (!queue.isEmpty()) {
let size = queue.size();
for (let i = 0; i < size; i++) {
const node = queue.pop();
if (node.left == null && node.right == null) return depth;
if (node.left) {
queue.push(node.left);
}
if (node.right) {
queue.push(node.right);
}
}
depth++;
}
return depth;
};
class Queue {
constructor() {
this.items = [];
this.count = 0;
this.lowerCount = 0;
}
push(elem) {
this.items[this.count++] = elem;
}
pop() {
if (this.isEmpty()) {
return;
}
const elem = this.items[this.lowerCount];
delete this.items[this.lowerCount];
this.lowerCount++;
return elem;
}
isEmpty() {
if (this.size() === 0) return true;
return false;
}
size() {
return this.count - this.lowerCount;
}
}
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【🔥】高频算法题系列:栈
主要有以下几类高频考题:
- 最小栈【简单】【栈】
- 有效的括号【中等】【栈】【面试真题】
- 简化路径【中等】【栈】
- 下一个更大元素 【系列】【栈】
最小栈【栈】
题解
→点击展开查看
/**
* initialize your data structure here.
*/
var MinStack = function() {
this.stack = [];
this.minArr = [];
this.count = 0;
this.min = Number.MAX_SAFE_INTEGER;
};
/**
* @param {number} x
* @return {void}
*/
MinStack.prototype.push = function(x) {
this.min = Math.min(this.min, x);
this.minArr[this.count] = this.min;
this.stack[this.count] = x;
this.count++;
};
/**
* @return {void}
*/
MinStack.prototype.pop = function() {
const element = this.stack[this.count - 1];
if (this.count - 2 >= 0) this.min = this.minArr[this.count - 2];
else this.min = Number.MAX_SAFE_INTEGER;
delete this.stack[this.count - 1];
delete this.minArr[this.count - 1];
this.count--;
return element;
};
/**
* @return {number}
*/
MinStack.prototype.top = function() {
if (this.count >= 1) {
return this.stack[this.count - 1];
}
return null;
};
/**
* @return {number}
*/
MinStack.prototype.getMin = function() {
const element = this.minArr[this.count - 1];
return element;
};
/**
* Your MinStack object will be instantiated and called as such:
* var obj = new MinStack()
* obj.push(x)
* obj.pop()
* var param_3 = obj.top()
* var param_4 = obj.getMin()
*/
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【系列】下一个更大元素 【栈】
受限于篇幅,这里只给出第一道题的代码模板
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number[]}
*/
var nextGreaterElements = function(nums) {
let ans = [];
let stack = new Stack();
const n = nums.length;
for (let i = 2 * n - 1; i >= 0; i--) {
while (!stack.isEmpty() && stack.top() <= nums[i % n]) {
stack.pop();
}
ans[i % n] = stack.isEmpty() ? -1 : stack.top();
stack.push(nums[i % n]);
}
return ans;
};
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
top() {
if (this.isEmpty()) return undefined;
return this.items[this.count - 1];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return undefined;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
isEmpty() {
return this.size() === 0;
}
size() {
return this.count;
}
}
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【面试真题】有效的括号【栈】
题解
→点击展开查看
/**
* @param {string} s
* @return {boolean}
*/
var isValid = function(s) {
if (s.length === 0) {
return true;
}
if (s.length % 2 !== 0) {
return false;
}
let map = {
')': '(',
']': '[',
'}': '{',
};
let left = ['(', '[', '{'];
let right = [')', ']', '}'];
let stack = new Stack();
for (let i = 0; i < s.length; i++) {
if (!right.includes(s[i])) {
stack.push(s[i]);
} else {
const matchStr = map[s[i]];
while (!stack.isEmpty()) {
const element = stack.pop();
if (left.includes(element) && matchStr !== element) return false;
if (element === matchStr) break;
}
}
}
return stack.isEmpty();
};
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return undefined;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
isEmpty() {
return this.size() === 0;
}
size() {
return this.count;
}
}
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简化路径【栈】
题解
→点击展开查看
/**
* @param {string} path
* @return {string}
*/
var simplifyPath = function(path) {
let newPath = path.split('/');
newPath = newPath.filter(item => item !== "");
const stack = new Stack();
for (let s of newPath) {
if (s === '..') stack.pop();
else if (s !== '.') stack.push(s);
}
if (stack.isEmpty()) return '/';
let str = '';
while (!stack.isEmpty()) {
const element = stack.pop();
str = '/' + element + str;
}
return str;
};
function handleBack(stack, tag, num) {
if (!stack.isEmpty()) return num;
const element = stack.pop();
if (element === '..') return handleBack(stack, tag, num + 1);
else {
stack.push(element);
return num;
}
}
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return undefined;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
size() {
return this.count;
}
isEmpty() {
return this.size() === 0;
}
}
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【🔥】高频算法题系列:DFS
主要有以下几类高频考题:
- 岛屿的最大面积【中等】【DFS】
- 相同的树【简单】【DFS】
岛屿的最大面积【DFS】
👉 【LeetCode 直通车】:695 岛屿的最大面积(中等)
题解
→点击展开查看
/**
* @param {number[][]} grid
* @return {number}
*/
let maxX, maxY;let visited;let globalMaxArea;
var maxAreaOfIsland = function(grid) {
visited = new Set();
maxX = grid.length;
maxY = grid[0].length;
globalMaxArea = 0;
for (let i = 0; i < maxX; i++) {
for (let j = 0; j < maxY; j++) {
if (grid[i][j] === 1) {
visited.add(`(${i}, ${j})`);
globalMaxArea = Math.max(globalMaxArea, dfs(grid, i, j));
}
visited.clear();
}
}
return globalMaxArea;
};
function dfs(grid, x, y) {
let res = 1;
for (let i = -1; i <= 1; i++) {
for (let j = -1; j <= 1; j++) {
if (Math.abs(i) === Math.abs(j)) continue;
const newX = x + i;
const newY = y + j;
if (newX >= maxX || newX < 0 || newY >= maxY || newY < 0) continue;
if (visited.has(`(${newX}, ${newY})`)) continue;
visited.add(`(${newX}, ${newY})`);
const areaCnt = grid[newX][newY]
if (areaCnt === 1) {
const cnt = dfs(grid, newX, newY);
res += cnt;
}
}
}
return res;
}
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相同的树【DFS】
题解
→点击展开查看
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} p
* @param {TreeNode} q
* @return {boolean}
*/
var isSameTree = function(p, q) {
if (p == null && q == null) return true;
if (p == null || q == null) return false;
if (p.val !== q.val) return false;
return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
};
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【🔥】高频算法题系列:回溯算法
主要有以下几类高频考题:
- N皇后【困难】【回溯算法】【面试真题】
- 全排列【中等】【回溯算法】
- 括号生成【中等】【回溯算法】
- 复原 IP 地址【中等】【回溯算法】
- 子集 【简单】【回溯算法】
【面试真题】N皇后【回溯算法】
题解
→点击展开查看
/**
* @param {number} n
* @return {string[][]}
*/
let result = [];
var solveNQueens = function(n) {
result = [];
let board = [];
for (let i = 0; i < n; i++) {
board[i] = [];
for (let j = 0; j < n; j++) {
board[i][j] = '.'
}
}
backtrack(0, board, n);
return result;
};
function deepClone(board) {
let res = [];
for (let i = 0; i < board.length; i++) {
res.push(board[i].join(''));
}
return res;
}
function backtrack(row, board, n) {
if (row === n) {
result.push(deepClone(board));
return;
}
for (let j = 0; j < n; j++) {
if (checkInValid(board, row, j, n)) continue;
board[row][j] = 'Q';
backtrack(row + 1, board, n);
board[row][j] = '.';
}
}
function checkInValid(board, row, column, n) {
// 行
for (let i = 0; i < n; i++) {
if (board[i][column] === 'Q') return true;
}
for (let i = row - 1, j = column + 1; i >= 0 && j < n; i--, j++) {
if (board[i][j] === 'Q') return true;
}
for (let i = row - 1, j = column - 1; i >= 0 && j >= 0; i--, j--) {
if (board[i][j] === 'Q') return true;
}
return false;
}
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全排列【回溯算法】
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number[][]}
*/
let results = [];var permute = function(nums) {
results = [];
backtrack(nums, []);
return results;
};
function backtrack(nums, track) {
if (nums.length === track.length) {
results.push(track.slice());
return;
}
for (let i = 0; i < nums.length; i++) {
if (track.includes(nums[i])) continue;
track.push(nums[i]);
backtrack(nums, track);
track.pop();
}
}
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括号生成【回溯算法】
题解
→点击展开查看
/**
* @param {number} n
* @return {string[]}
*/
var generateParenthesis = function(n) {
let validRes = [];
backtrack(n * 2, validRes, '');
return validRes;
};
function backtrack(len, validRes, bracket) {
if (bracket.length === len) {
if (isValidCombination(bracket)) {
validRes.push(bracket);
}
return;
}
for (let str of ['(', ')']) {
bracket += str;
backtrack(len, validRes, bracket);
bracket = bracket.slice(0, bracket.length - 1);
}
}
function isValidCombination(bracket) {
let stack = new Stack();
for (let i = 0; i < bracket.length; i++) {
const str = bracket[i];
if (str === '(') {
stack.push(str);
} else if (str === ')') {
const top = stack.pop();
if (top !== '(') return false;
}
}
return stack.isEmpty();
}
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
size() {
return this.count;
}
isEmpty() {
return this.size() === 0;
}
}
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复原 IP 地址【回溯算法】
👉 【LeetCode 直通车】:93 复原 IP 地址(中等)
题解
→点击展开查看
/**
* @param {string} s
* @return {string[]}
*/
var restoreIpAddresses = function(s) {
if (s.length > 12) return [];
let res = [];
const track = [];
backtrack(s, track, res);
return res;
};
function backtrack(s, track, res) {
if (track.length === 4 && s.length === 0) {
res.push(track.join('.'));
return;
}
let len = s.length >= 3 ? 3 : s.length;
for (let i = 0; i < len; i++) {
const c = s.slice(0, i + 1);
if (parseInt(c) > 255) continue;
if (i >= 1 && parseInt(c) < parseInt((1 + '0'.repeat(i)))) continue;
track.push(c);
backtrack(s.slice(i + 1), track, res);
track.pop();
}
}
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子集【回溯算法】
题解
→点击展开查看
/**
* @param {number[]} nums
* @return {number[][]}
*/
var subsets = function(nums) {
if (nums.length === 0) return [[]];
let resArr = [];
backtrack(nums, 0, [], resArr);
return resArr;
};
function backtrack(nums, index, subArr, resArr) {
if (Array.isArray(subArr)) {
resArr.push(subArr.slice());
}
if (index === nums.length) {
return;
}
for (let i = index; i < nums.length; i++) {
subArr.push(nums[i]);
backtrack(nums, i + 1, subArr, resArr);
subArr.pop(nums[i]);
}
}
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原文地址 干货文章分享 - 字节跳动最常考的 64 道JS算法题
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