1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
#include <iostream>
#include <stdio.h>
#define N 200000

using namespace std;

int f(char c)
{
    if(c=='C') return 0;
    if(c=='Z') return 1;
    return 2;
}

int n,q;
int a[N+1],p[3][2];
long long M=1000000007,inv2=500000004,pw=1;
long long dp[N+1][3];
int idx;
char ch;

long long res()
{
    /*cout<<"res()"<<endl;
    for(int i=0;i<3;i++)
    {
        cout<<p[i][0]<<" "<<p[i][1]<<endl;
    }*/
    int d=abs(p[0][0]+p[0][1]-p[1][0]-p[1][1])%3;
    //cout<<d<<endl;

    long long r=(pw-dp[p[2][0]+p[2][1]][d]+M)%M;
    if((n&1)&&(n>1))
    {
        if(p[0][0]==0&&p[1][1]==0) r--;
        if(p[0][1]==0&&p[1][0]==0) r--;
        r=(r+M)%M;
    }

    return r;
}

int main()
{
    dp[0][0]=1;
    for(int i=1;i<=N;i++)
    {
        dp[i][0]=(dp[i-1][1]+dp[i-1][2])%M;
        dp[i][1]=(dp[i-1][2]+dp[i-1][0])%M;
        dp[i][2]=(dp[i-1][0]+dp[i-1][1])%M;
        //if(i<10) cout<<dp[i][0]<<" "<<dp[i][1]<<" "<<dp[i][2]<<endl;
    }

    scanf("%d%d\n",&n,&q);
    for(int i=0;i<n;i++)
    {
        a[i]=f(getchar());
        p[a[i]][i&1]++;
        if(a[i]==2) pw=(pw*2)%M;
    }

    printf("%lld\n",res());

    for(int i=0;i<q;i++)
    {
        scanf("%d %c\n",&idx,&ch);
        idx--;
        p[a[idx]][idx&1]--;
        if(a[idx]==2) pw=(pw*inv2)%M;

        a[idx]=f(ch);
        p[a[idx]][idx&1]++;
        if(a[idx]==2) pw=(pw*2)%M;

        printf("%lld\n",res());
    }

    return 0;
}