class Solution {
public int peakIndexInMountainArray(int[] arr) {
//二分查找试试,修改边界的条件要变动一下
int l = 1;
int r = arr.length-2;
while(l<=r){
int mid = (r+l)/2;
if(arr[mid]>arr[mid-1]) l=mid+1;
//中间的大于前面的 说明山峰在右半部分 调整左边界
else r = mid-1;
}
return r;
}
}