GenomicRangeQuery【★★★★★】

        /// <summary>
        /// Solution - Prefix Sums
        /// 100/100
        /// </summary>
        /// <param name="S"></param>
        /// <param name="P"></param>
        /// <param name="Q"></param>
        /// <returns></returns>
        public static int[] solution(string S, int[] P, int[] Q)
        {
            int length = S.Length;
            int[] result = new int[P.Length];
            int[,] arr = new int[length, 4];

            for (int i = 0; i < length; i++)
            {
                if (S[i] == 'A') arr[i, 0] = 1;
                if (S[i] == 'C') arr[i, 1] = 1;
                if (S[i] == 'G') arr[i, 2] = 1;
                if (S[i] == 'T') arr[i, 3] = 1;
            }

            //compute prefixes
            for (int i = 1; i < length; i++)
            {
                for (int j = 0; j < 4; j++)
                {
                    arr[i, j] += arr[i - 1, j];
                }
            }

            for (int i = 0; i < P.Length; i++)
            {
                int x = P[i];
                int y = Q[i];
                for (int j = 0; j < 4; j++)
                {
                    int sub = 0;
                    if (x - 1 >= 0)
                        sub = arr[x - 1, j];
                    if (arr[y, j] - sub > 0)
                    {
                        result[i] = j + 1;
                        break;
                    }
                }
            }

            return result;
        }