Problem:
Score : 400 points

Problem Statement

The ABC number of a string T is the number of triples of integers (i, j, k) that satisfy all of the following conditions:

1 ≤ i < j < k ≤ |T| (|T| is the length of T.)

T_i = A (T_i is the i-th character of T from the beginning.)

T_j = B

T_k = C

For example, when T = ABCBC, there are three triples of integers (i, j, k) that satisfy the conditions: (1, 2, 3), (1, 2, 5), (1, 4, 5). Thus, the ABC number of T is 3.

You are given a string S. Each character of S is A, B, C or ?.

Let Q be the number of occurrences of ? in S. We can make 3^Q strings by replacing each occurrence of ? in S with A, B or C. Find the sum of the ABC numbers of all these strings.

This sum can be extremely large, so print the sum modulo 10^9 + 7.

Constraints

3 ≤ |S| ≤ 10^5

Each character of S is A, B, C or ?.

Input

Input is given from Standard Input in the following format:

S

Output

Print the sum of the ABC numbers of all the 3^Q strings, modulo 10^9 + 7.

Sample Input 1

A??C

Sample Output 1

8

In this case, Q = 2, and we can make 3^Q = 9 strings by by replacing each occurrence of ? with A, B or C. The ABC number of each of these strings is as follows:

AAAC: 0

AABC: 2

AACC: 0

ABAC: 1

ABBC: 2

ABCC: 2

ACAC: 0

ACBC: 1

ACCC: 0

The sum of these is 0 + 2 + 0 + 1 + 2 + 2 + 0 + 1 + 0 = 8, so we print 8 modulo 10^9 + 7, that is, 8.

Sample Input 2

ABCBC

Sample Output 2

3

When Q = 0, we print the ABC number of S itself, modulo 10^9 + 7. This string is the same as the one given as an example in the problem statement, and its ABC number is 3.

Sample Input 3

????C?????B??????A???????

Sample Output 3

979596887

In this case, the sum of the ABC numbers of all the 3^Q strings is 2291979612924, and we should print this number modulo 10^9 + 7, that is, 979596887.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;

namespace D
{
    class Program
    {
        private static readonly long MOD = 1000000007;

        static void Main(string[] args)
        {
            string S = Console.ReadLine();
            long[,] dp = new long[S.Length + 1, 4];
            dp[0, 0] = 1;
            for (var i = 1; i <= S.Length; i++)
            {
                if ('A' == S[i - 1])
                    dp[i, 1] += dp[i - 1, 0];
                if ('B' == S[i - 1])
                    dp[i, 2] += dp[i - 1, 1];
                if ('C' == S[i - 1])
                    dp[i, 3] += dp[i - 1, 2];
                if (S[i - 1] == '?')
                {
                    dp[i, 0] += 3 * dp[i - 1, 0];
                    dp[i, 1] += 3 * dp[i - 1, 1];
                    dp[i, 2] += 3 * dp[i - 1, 2];
                    dp[i, 3] += 3 * dp[i - 1, 3];
                    dp[i, 1] += dp[i - 1, 0];
                    dp[i, 2] += dp[i - 1, 1];
                    dp[i, 3] += dp[i - 1, 2];
                }
                else
                {
                    dp[i, 0] += dp[i - 1, 0];
                    dp[i, 1] += dp[i - 1, 1];
                    dp[i, 2] += dp[i - 1, 2];
                    dp[i, 3] += dp[i - 1, 3];
                }

                dp[i, 0] %= MOD;
                dp[i, 1] %= MOD;
                dp[i, 2] %= MOD;
                dp[i, 3] %= MOD;
            }
            Console.WriteLine(dp[S.Length, 3]);
        }
    }
}