二分查找一＞山脉数组的峰顶索引

public int peakIndexInMountainArray(int[] arr) {
        int left = 1, right = arr.length-2;

        while(left < right) {
            int mid = left + (right-left+1) / 2;
            if(arr[mid] > arr[mid-1]) left = mid;
            else  right = mid-1;
        }
        return left;
    }