852. Peak Index in a Mountain Array

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

//O(log(A.size()) - time complexity, O(A.size()) - memory complexity