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Commit ce9c981

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scuyjzh
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add solutions to problem - "845. Longest Mountain in Array"
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‎README.md‎

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| 42 | [接雨水](https://leetcode-cn.com/problems/trapping-rain-water/) | [Java](./src/com/scuyjzh/leetcode/hard/No_0042_Trapping_Rain_Water/Solution.java) | 困难 | 栈 数组 双指针 动态规划 单调栈 |
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| 658 | [找到 K 个最接近的元素](https://leetcode-cn.com/problems/find-k-closest-elements/) | [Java](./src/com/scuyjzh/leetcode/medium/No_0658_Find_K_Closest_Elements/Solution.java) | 中等 | 数组 双指针 二分查找 排序 堆(优先队列) |
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| 259 | [较小的三数之和](https://leetcode-cn.com/problems/3sum-smaller/) 🔒 | [Java](./src/com/scuyjzh/leetcode/medium/No_0259_3Sum_Smaller/Solution.java) | 中等 | 数组 双指针 二分查找 排序 |
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| 845 | [数组中的最长山脉](https://leetcode-cn.com/problems/longest-mountain-in-array/) | [Java](./src/com/scuyjzh/leetcode/medium/No_0845_Longest_Mountain_in_Array/Solution.java) | 中等 | 数组 双指针 动态规划 枚举 |
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### Array
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package com.scuyjzh.leetcode.medium.No_0845_Longest_Mountain_in_Array;
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/**
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* 845. 数组中的最长山脉
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*
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* 把符合下列属性的数组 arr 称为 山脉数组 :
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* • arr.length >= 3
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* • 存在下标 i(0 < i < arr.length - 1),满足
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* ○しろまる arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
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* ○しろまる arr[i] > arr[i + 1] > ... > arr[arr.length - 1]
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*
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* 给出一个整数数组 arr,返回最长山脉子数组的长度。如果不存在山脉子
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* 数组,返回 0 。
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*/
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class Solution {
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/**
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* 方法:双指针
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*/
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public int longestMountain(int[] arr) {
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int n = arr.length;
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int res = 0;
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int left = 0, right;
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while (left + 2 < n) {
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right = left + 1;
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// 山脉开始一定上升
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if (arr[left] < arr[left + 1]) {
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// 找到山顶
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while (right + 1 < n && arr[right] < arr[right + 1]) {
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++right;
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}
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// 山顶之后必须下降
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if (right + 1 < n && arr[right] > arr[right + 1]) {
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while (right + 1 < n && arr[right] > arr[right + 1]) {
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++right;
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}
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res = Math.max(res, right - left + 1);
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}
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}
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left = right;
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}
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return res;
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}
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public static void main(String[] args) {
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System.out.println(new Solution().longestMountain(new int[]{2, 1, 4, 7, 3, 2, 5}));
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}
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}

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