852.Peak-Index-in-a-Mountain-Array.cpp

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