###### tags: `LeetCode` `Binary Search` `Easy`
# LeetCode #852 [Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/)
### (Medium)

與[#162](https://hackmd.io/Pymu5cNRRziTRYo0GxeNoA)一樣

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) {
        int l=0, r=arr.size()-1;
        while(l<r){
            int m=l+(r-l+1)/2;
            if(arr[m]<=(m-1>=0?arr[m-1]:INT_MIN))r=m-1;
            else l=m;
        }
        return l;
    }
};