852. 山脉数组的峰顶索引

思路

二分查找，O(logN)

class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 0, right = arr.length - 1;
        int index = 0;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (arr[mid] < arr[mid + 1]) {
                left = mid + 1;
            } else {
                index = mid; // 记录
                right = mid - 1;// 再向左靠拢
            }
        }
        return index;
    }
}