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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

class Main {
  public static void main(String[] args) {
    long N = 1_000_000_007L;
    Scanner scanner = new Scanner(System.in);
    String str = scanner.next();

    long[][] d = new long[str.length() + 1][4];
    d[0][0] = 1;
    for (int i = 1; i <= str.length(); i++) {
      char ch = str.charAt(i - 1);

      int n = ch == '?' ? 3 : 1;
      int a = 0, b = 0, c = 0;
      if (ch == 'A' || ch == '?') a = 1;
      if (ch == 'B' || ch == '?') b = 1;
      if (ch == 'C' || ch == '?') c = 1;
      d[i][0] = d[i - 1][0] * n % N;
      d[i][1] = d[i - 1][1] * n % N + a * d[i - 1][0];
      d[i][2] = d[i - 1][2] * n % N + b * d[i - 1][1];
      d[i][3] = d[i - 1][3] * n % N + c * d[i - 1][2];

      for (int j = 0; j < 4; j++) d[i][j] %= N;
    }

    System.out.println(d[str.length()][3]);
  }
}