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Commit ef8cc67

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update 2 leetcode
1 parent 2bc50eb commit ef8cc67

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2 files changed

+174
-5
lines changed

2 files changed

+174
-5
lines changed
Lines changed: 104 additions & 0 deletions
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/*
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* @lc app=leetcode id=102 lang=javascript
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*
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* [102] Binary Tree Level Order Traversal
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* function TreeNode(val, left, right) {
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* this.val = (val===undefined ? 0 : val)
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* this.left = (left===undefined ? null : left)
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* this.right = (right===undefined ? null : right)
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* }
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*/
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/**
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* 递归的方式
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* @param {TreeNode} root
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* @return {number[][]}
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*/
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var levelOrder = function(root) {
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function map(root, res = [], level = 0) {
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if (!root) {
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return []; // 根节点为空的情况
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}
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res[level] = res[level] || [];
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res[level].push(root.val);
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root.left && map(root.left, res, level + 1);
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root.right && map(root.right, res, level + 1);
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return res;
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}
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return map(root);
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};
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/**
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* 迭代遍历的方式
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* @param {TreeNode} root
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* @return {number[][]}
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*/
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var levelOrder2 = function(root) {
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let queues = [root];
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let level = 0;
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let res = [];
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while (queues.length) {
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// 当前层级的长度
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let len = queues.length;
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// 遍历同一个层级
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while (len--) {
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const cur = queues.shift();
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// 不存在就直接跳过
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if (!cur) {
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continue;
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}
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if (cur.val !== null) {
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res[level] = res[level] || [];
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res[level].push(cur.val);
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}
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cur.left && queues.push(cur.left);
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cur.right && queues.push(cur.right);
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}
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level++;
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}
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return res;
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};
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/**
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* 迭代声明的方式,但是少声明一个变量
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* @param {*} root
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* @returns
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*/
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var levelOrder3 = function(root) {
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// 下文是默认推入数组的,所以对没有数据的需要单独判断
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if (!root) {
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return [];
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}
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let queues = [root];
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let res = [];
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while (queues.length) {
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// 当前层级的长度
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let len = queues.length;
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res.push([]);
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// 遍历同一个层级
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while (len--) {
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const cur = queues.shift();
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// 不存在就直接跳过
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if (!cur) {
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continue;
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}
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if (cur.val !== null) {
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res[res.length - 1] = res[res.length - 1] || [];
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res[res.length - 1].push(cur.val);
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}
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cur.left && queues.push(cur.left);
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cur.right && queues.push(cur.right);
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}
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}
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return res;
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};
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// @lc code=end

‎leetcode/70.climbing-stairs.js

Lines changed: 70 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -6,16 +6,81 @@
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// @lc code=start
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/**
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* 这个方式比较巧妙,使用的是动态规划
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* @param {number} n
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* @return {number}
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*/
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var climbStairs2 = function(n) {
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let p = q = 0, r = 1;
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// 这里的核心是 f(x) = f(x - 1) + f(x - 2) 这套公式
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// 在不断的循环中,去更新这几个
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for (let i = 0; i < n; i++) {
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p = q;
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q = r;
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r = p + q;
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}
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return r;
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};
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/**
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* 这是尾递归版本,内存优化较好
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* @param {*} n
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* @returns
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*/
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var climbStairs = function(n) {
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if (n === 1) {
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return 1;
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/**
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* 这里是采用优化版本的递归方式
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*/
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let fibonacci = function (n, n1 = 1, n2 = 1) {
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if (n <= 1) {
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return n2;
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}
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if (n === 2) {
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return 2;
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return fibonacci(n - 1, n2, n1 + n2);
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}
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return fibonacci(n);
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};
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/**
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* 这是递归版本,但做了缓存优化
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* @param {*} n
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* @returns
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*/
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var climbStairs3 = function(n) {
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/**
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* 这里是采用优化版本的递归方式
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*/
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let fibonacci = (function () {
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// 使用对象来缓存数据,防止重复计算
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let memory = {};
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return function (n) {
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if (memory[n] !== undefined) {
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return memory[n];
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}
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return memory[n] = n === 1 || n === 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
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}
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return climbStairs(n - 1) + climbStairs(n - 2);
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})();
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return fibonacci(n);
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// 下面是未优化的版本,内存效率很低
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// if (n === 1 || n === 2) {
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// return 1;
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// }
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// if (n === 2) {
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// return 2;
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// }
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// return climbStairs(n - 1) + climbStairs(n - 2);
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};
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// @lc code=end
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/**
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* 斐波那契数列的求和方式
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*/
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let fibonacci = (function () {
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let memory = {};
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return function (n) {
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if (memory[n] !== undefined) {
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return memory[n];
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}
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return memory[n] = n === 1 || n === 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
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}
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})();

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