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Commit 4217b25

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Merge pull request SharingSource#534 from SharingSource/ac_oier
✨feat: add 560
2 parents 5268b82 + ed9081f commit 4217b25

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‎Index/前缀和.md‎

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| [523. 连续的子数组和](https://leetcode-cn.com/problems/continuous-subarray-sum/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/continuous-subarray-sum/solution/gong-shui-san-xie-tuo-zhan-wei-qiu-fang-1juse/) | 中等 | 🤩🤩🤩🤩 |
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| [525. 连续数组](https://leetcode-cn.com/problems/contiguous-array/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/contiguous-array/solution/gong-shui-san-xie-qian-zhui-he-ha-xi-bia-q400/) | 中等 | 🤩🤩🤩🤩 |
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| [528. 按权重随机选择](https://leetcode-cn.com/problems/random-pick-with-weight/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/random-pick-with-weight/solution/gong-shui-san-xie-yi-ti-shuang-jie-qian-8bx50/) | 中等 | 🤩🤩🤩🤩 |
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| [560. 和为 K 的子数组](https://leetcode.cn/problems/subarray-sum-equals-k/) | [LeetCode 题解链接](https://leetcode.cn/problems/subarray-sum-equals-k/solution/by-ac_oier-pttu/) | 中等 | 🤩🤩🤩🤩🤩 |
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| [629. K个逆序对数组](https://leetcode-cn.com/problems/k-inverse-pairs-array/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/k-inverse-pairs-array/solution/gong-shui-san-xie-yi-dao-xu-lie-dp-zhuan-tm01/) | 中等 | 🤩🤩🤩🤩🤩 |
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| [661. 图片平滑器](https://leetcode-cn.com/problems/image-smoother/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/image-smoother/solution/by-ac_oier-nn3v/) | 简单 | 🤩🤩🤩🤩 |
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| [689. 三个无重叠子数组的最大和](https://leetcode-cn.com/problems/maximum-sum-of-3-non-overlapping-subarrays/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/maximum-sum-of-3-non-overlapping-subarrays/solution/gong-shui-san-xie-jie-he-qian-zhui-he-de-ancx/) | 困难 | 🤩🤩🤩 |

‎Index/哈希表.md‎

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| [500. 键盘行](https://leetcode-cn.com/problems/keyboard-row/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/keyboard-row/solution/gong-shui-san-xie-jian-dan-zi-fu-chuan-m-zx6b/) | 简单 | 🤩🤩🤩🤩 |
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| [519. 随机翻转矩阵](https://leetcode-cn.com/problems/random-flip-matrix/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/random-flip-matrix/solution/gong-shui-san-xie-note-bie-pian-yi-ti-sh-e6gi/) | 中等 | 🤩🤩🤩🤩 |
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| [554. 砖墙](https://leetcode-cn.com/problems/brick-wall/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/brick-wall/solution/gong-shui-san-xie-zheng-nan-ze-fan-shi-y-gsri/) | 中等 | 🤩🤩🤩 |
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| [560. 和为 K 的子数组](https://leetcode.cn/problems/subarray-sum-equals-k/) | [LeetCode 题解链接](https://leetcode.cn/problems/subarray-sum-equals-k/solution/by-ac_oier-pttu/) | 中等 | 🤩🤩🤩🤩🤩 |
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| [594. 最长和谐子序列](https://leetcode-cn.com/problems/longest-harmonious-subsequence/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/longest-harmonious-subsequence/solution/gong-shui-san-xie-yi-ti-shuang-jie-hua-d-quuh/) | 简单 | 🤩🤩🤩🤩 |
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| [599. 两个列表的最小索引总和](https://leetcode-cn.com/problems/minimum-index-sum-of-two-lists/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/minimum-index-sum-of-two-lists/solution/by-ac_oier-oh5b/) | 简单 | 🤩🤩🤩🤩 |
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| [645. 错误的集合](https://leetcode-cn.com/problems/set-mismatch/) | [LeetCode 题解链接](https://leetcode-cn.com/problems/set-mismatch/solution/gong-shui-san-xie-yi-ti-san-jie-ji-shu-s-vnr9/) | 简单 | 🤩🤩🤩 |
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### 题目描述
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这是 LeetCode 上的 **[560. 和为 K 的子数组](https://leetcode.cn/problems/subarray-sum-equals-k/solution/by-ac_oier-pttu/)** ,难度为 **中等**。
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Tag : 「前缀和」、「哈希表」
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给你一个整数数组 `nums` 和一个整数 `k` ,请你统计并返回该数组中和为 `k` 的子数组的个数 。
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示例 1:
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```
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输入:nums = [1,1,1], k = 2
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输出:2
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```
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示例 2:
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```
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输入:nums = [1,2,3], k = 3
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输出:2
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```
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提示:
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* 1ドル <= nums.length <= 2 * 10^4$
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* $-1000 <= nums[i] <= 1000$
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* $-10^7 <= k <= 10^7$
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---
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### 前缀和 + 哈希表
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这是一道经典的前缀和运用题。
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统计以每一个 $nums[i]$ 为结尾,和为 $k$ 的子数组数量即是答案。
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我们可以预处理前缀和数组 `sum`(前缀和数组下标默认从 1ドル$ 开始),对于求解以某一个 $nums[i]$ 为结尾的,和为 $k$ 的子数组数量,本质上是求解在 $[0, i]$ 中,`sum` 数组中有多少个值为 $sum[i + 1] - k$ 的数,这可以在遍历过程中使用「哈希表」进行同步记录。
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代码:
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```Java
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class Solution {
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public int subarraySum(int[] nums, int k) {
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int n = nums.length, ans = 0;
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int[] sum = new int[n + 10];
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for (int i = 1; i <= n; i++) sum[i] = sum[i - 1] + nums[i - 1];
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Map<Integer, Integer> map = new HashMap<>();
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map.put(0, 1);
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for (int i = 1; i <= n; i++) {
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int t = sum[i], d = t - k;
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ans += map.getOrDefault(d, 0);
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map.put(t, map.getOrDefault(t, 0) + 1);
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}
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return ans;
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}
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}
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```
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* 时间复杂度:预处理前缀和的复杂度为 $O(n),ドル统计答案的复杂度为 $O(n)$。整体复杂度为 $O(n)$
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* 空间复杂度:$O(n)$
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---
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### 最后
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这是我们「刷穿 LeetCode」系列文章的第 `No.560` 篇,系列开始于 2021年01月01日,截止于起始日 LeetCode 上共有 1916 道题目,部分是有锁题,我们将先把所有不带锁的题目刷完。
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在这个系列文章里面,除了讲解解题思路以外,还会尽可能给出最为简洁的代码。如果涉及通解还会相应的代码模板。
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为了方便各位同学能够电脑上进行调试和提交代码,我建立了相关的仓库:https://github.com/SharingSource/LogicStack-LeetCode 。
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在仓库地址里,你可以看到系列文章的题解链接、系列文章的相应代码、LeetCode 原题链接和其他优选题解。
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‎LeetCode/剑指 Offer II/剑指 Offer II 114. 外星文字典(困难).md‎

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@@ -49,7 +49,7 @@ Tag : 「图论」、「拓扑排序」、「建图」、「图论 BFS」
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为了方便,我们称 `words` 为 `ws`,同时将两个字符串 `a` 和 `b` 之间的字典序关系简称为「关系」。
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由于数组长度和每个 $ws[i]$ 的最大长度均为 100ドル,ドル我们可以实现复杂度为 $O(n^3)$ 复杂度的算法。
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由于数组长度和每个 $ws[i]$ 的最大长度均为 100ドル,ドル我们可以实现复杂度为 $O(n^3)$ 的算法。
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首先容易想到,我们从前往后处理每个 $ws[i],ドル利用 `ws` 数组本身已按字典序排序,然后通过 $ws[i]$ 与 $ws[j]$ 的关系(其中 $j$ 的范围为 $[0, i - 1]$),来构建字符之间的关系。
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int N = 26, M = N * N, idx = 0, cnt = 0;
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int[] he = new int[N], e = new int[M], ne = new int[M];
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int[] in = new int[N], out = new int[N];
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boolean[] vis = new boolean[26];
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boolean[] vis = new boolean[N];
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void add(int a, int b) {
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e[idx] = b;
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ne[idx] = he[a];

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