class Solution {
public:
    int peakIndexInMountainArray(const vector<int>& A) {
        int left = 0;
        int right = A.size() - 1;

        while (right - left > 1) {
            int mid = (left + right) / 2;

            if (A[mid] < A[mid + 1]) {
                left = mid;
            } else {
                right = mid;
            }
        }
        return right;
    }
};