leetcode-941-easy

Valid Mountain Array

Given an array of integers arr, return true if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:

arr.length >= 3
There exists some i with 0 < i < arr.length - 1 such that:
arr[0] < arr[1] < ... < arr[i - 1] < arr[i] 
arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Example 1:

Input: arr = [2,1]
Output: false
Example 2:

Input: arr = [3,5,5]
Output: false
Example 3:

Input: arr = [0,3,2,1]
Output: true
Constraints:

1 <= arr.length <= 104
0 <= arr[i] <= 104

思路一：设置 low, high 两个指针，分别指向数组的头尾，模拟数组递增，递减操作，最后比较 low, high 是否相等

    public boolean validMountainArray(int[] arr) {
        int low = 0;
        int high = arr.length - 1;

        while (low < arr.length - 1) {
            if (arr[low] >= arr[low + 1]) {
                break;
            }
            low++;
        }

        while (high > 0) {
            if (arr[high - 1] <= arr[high]) {
                break;
            }
            high--;
        }

        return low > 0 && high < arr.length - 1 && low == high;
    }