class Solution {

public:

    int numberOfArithmeticSlices(vector<int>& A)

    {

        int res = 0, n = A.size();

        vector<unordered_map<int, int>> dp(n);

        for (int i = 0; i < n; ++i)

        {

            for (int j = 0; j < i; ++j)

            {

                long delta = (long)A[i] - A[j];

                if (delta > INT_MAX || delta < INT_MIN)

                {

                    continue;

                }

                int diff = (int)delta;

                ++dp[i][diff];

                if (dp[j].count(diff))

                {

                    res += dp[j][diff];

                    dp[i][diff] += dp[j][diff];

                }

            }

        }

        return res;

    }

};