852. Peak Index in a Mountain Array

https://leetcode.com/problems/peak-index-in-a-mountain-array/

1. Use binary search:

//12 ms    7.2 MB
class Solution {
public:
    int peakIndexInMountainArray(vector<int>& A) {
        int l = 0;
        int r = A.size() - 1;
        while(l < r){
            int median = l + (r - l) / 2;
            if(A[median] < A[median + 1])
                l = median + 1;
            else if(A[median] > A[median + 1])
                r = median;
        }
        return l;
    }
};