852.山脉数组的峰顶索引，简单易懂0ms

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