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 Ruby (2.3.3) (judge verdict: Accepted)

S = gets.chomp
N = S.length

MOD = 10**9+7

a = Array.new(N+1, 0)
c = Array.new(N+1, 0)

sum = 1
N.times do |i|
    if S[i] == 'A'
        a[i] = a[i-1] + sum
    elsif S[i] == '?'
        a[i] = 3*a[i-1] + sum
        sum = sum * 3 % MOD
    else
        a[i] = a[i-1]
    end
    a[i] %= MOD
end

sum = 1
(N-1).downto(0) do |i|
    if S[i] == 'C'
        c[i] = c[i+1] + sum
    elsif S[i] == '?'
        c[i] = 3*c[i+1] + sum
        sum = sum * 3 % MOD
    else
        c[i] = c[i+1]
    end
    c[i] %= MOD
end

ans = 0
(1..(N-2)).each do |i|
    if S[i] == 'B' || S[i] == '?'
        ans += a[i-1] * c[i+1]
        ans %= MOD
    end
end
puts ans