Algorithm to calculate number of intersecting discs

Question

Given an array A of N integers we draw N discs in a 2D plane, such that i-th disc has center in (0,i) and a radius

Answer 1

100% score in Codility.

Here is an adaptation to C# of Толя solution:

    public int solution(int[] A)
    {
        long result = 0;
        Dictionary dps = new Dictionary();
        Dictionary dpe = new Dictionary();

        for (int i = 0; i < A.Length; i++)
        {
            Inc(dps, Math.Max(0, i - A[i]));
            Inc(dpe, Math.Min(A.Length - 1, i + A[i]));
        }

        long t = 0;
        for (int i = 0; i < A.Length; i++)
        {
            int value;
            if (dps.TryGetValue(i, out value))
            {
                result += t * value;
                result += value * (value - 1) / 2;
                t += value;
                if (result > 10000000)
                    return -1;
            }
            dpe.TryGetValue(i, out value);
            t -= value;
        }

        return (int)result;
    }

    private static void Inc(Dictionary values, long index)
    {
        int value;
        values.TryGetValue(index, out value);
        values[index] = ++value;
    }