https://leetcode.cn/problems/valid-mountain-array/description/

双指针

class Solution {public boolean validMountainArray(int[] arr) {int len=arr.length;if(len<3) return false;int left=0,right=len-1;while(left+1<len&&arr[left]<arr[left+1]){left++;}while(right-1>=0&&arr[right-1]>arr[right]){right--;}//指针相遇if(left==right&&left!=0&&left!=len-1){return true;}return false;}
}

暴力

class Solution {public boolean validMountainArray(int[] arr) {int len=arr.length;if(len<3) return false;for(int i=1;i<len-1;i++){int cur=i;int before=i-1;while(before>=0&&arr[before]<arr[cur]){cur--;before--;}if(before>=0) continue;//跳过这个数cur=i;int after=i+1;while(after<len&&arr[cur]>arr[after]){cur++;after++;}if(after<len) continue;return true;}return false;}
}
//左边的都小于它，右边的都大于它