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

        while (left <= right) {
             int mid = left + (right - left) / 2;
                if (A[mid - 1] < A[mid] && A[mid + 1] < A[mid]) {
                    return mid;
                }
            if (A[mid] < A[mid + 1]) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }

        return 0;
}
};