class Solution {
public:
    /**
     * @param A: An integers array.
     * @return: return any of peek positions.
     */
    int findPeak(vector<int> A) {
        // write your code here
        int size = A.size();
        if (size == 0) {
            return -1;
        }

        int start = 0;
        int end = size - 1;

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

        if (A[start] > A[end]) {
            return start;
        } else {
            return end;
        }
    }
};