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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MOD = 1000000007;
int main(void){
    string s; cin>>s;
    int L = s.size();
    vector <vector<ll>> dp(100010 ,vector <ll>(4,0));
    dp[0][0] = 1;
    for(int i=0;i<L;i++){
        if(s[i]=='?'){
            dp[i+1][0] += 3*dp[i][0]%MOD;
            dp[i+1][1] += 3*dp[i][1]%MOD;
            dp[i+1][2] += 3*dp[i][2]%MOD;
            dp[i+1][3] += 3*dp[i][3]%MOD;
        }
        else{
            dp[i+1][0] += dp[i][0]%MOD;
            dp[i+1][1] += dp[i][1]%MOD;
            dp[i+1][2] += dp[i][2]%MOD;
            dp[i+1][3] += dp[i][3]%MOD;
        }
        if(s[i]=='A'||s[i]=='?') {dp[i+1][1]+= dp[i][0]; dp[i+1][1]%=MOD;}
        if(s[i]=='B'||s[i]=='?') {dp[i+1][2]+= dp[i][1]; dp[i+1][2]%=MOD;}
        if(s[i]=='C'||s[i]=='?') {dp[i+1][3]+= dp[i][2]; dp[i+1][3]%=MOD;}
        
                    
    }
    cout<<dp[L][3]<<endl;
}