[LeetCode] 852. 山脉数组的峰顶索引

二分的一种变种，这次是比较条件改变了，相邻的两位来比较，进而判断左右区间的选择

class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int n = arr.length;
        int left = 1, right = n - 2, ans = 0;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (arr[mid] > arr[mid + 1]) {
                ans = mid;
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return ans;
    }
}