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
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
#include <bits/stdc++.h>
#define dbg(x) " [" << #x << ": " << (x) << "] "
using namespace std;
template<typename A,typename B>
ostream& operator<<(ostream& out,const pair<A,B>& p) {
    return out << "(" << p.first << ", " << p.second << ")";
}
template<typename T>
ostream& operator<<(ostream& out,const vector<T>& c) {
    out << "{";
    for(auto it = c.begin(); it != c.end(); it++) {
        if(it != c.begin()) out << ", ";
        out << *it;
    }
    return out << "}";
}
string s;
int n, b;
int r[2];
int g[2];
vector<vector<int>> f;
void add(int i) {
    if(s[i] == 'C') {
        r[i & 1]++;
    } else if(s[i] == 'Z') {
        g[i & 1]++;
    } else {
        b++;
    }
}
void del(int i) {
    if(s[i] == 'C') {
        r[i & 1]--;
    } else if(s[i] == 'Z') {
        g[i & 1]--;
    } else {
        b--;
    }
}
const int mod = 1e9 + 7;
void print() {
    int ans;
    if(n == 1) {
        ans = (b == 1 ? 2 : 1);
    } else {
        int x = (r[0] + r[1] + 2 * (g[0] + g[1]) + b) % 3;
        x = (3 - x) % 3;
        ans = (f[b][(x + 1) % 3] + f[b][(x + 2) % 3]) % mod;
        if(r[0] && r[1]) {
        } else if(g[0] && g[1]) {
        } else if(r[0] && g[0]) {
        } else if(r[1] && g[1]) {
        } else if(b == n) {
            if((n + n / 2) % 3 != 0) {
                ans = (ans + mod - 1) % mod;
            }
            if((n + (n + 1) / 2) % 3 != 0) {
                ans = (ans + mod - 1) % mod;
            }
        } else {
            int gr = (n + 1) / 2;
            if(r[0] || g[1]) {
                gr = n / 2;
            }
            if((n + gr) % 3 != 0) {
                ans = (ans + mod - 1) % mod;
            }
        }
    }
    cout << ans << '\n';
}
void solve() {
    int q;
    cin >> n >> q;
    cin >> s;
    f.resize(n + 1);
    f[0] = {1, 0, 0};
    for(int i = 1; i < n + 1; i++) {
        f[i].resize(3);
        for(int j = 0; j < 3; j++) {
            f[i][j] = (f[i - 1][j] + f[i - 1][(j + 2) % 3]) % mod;
        }
    }
    r[0] = r[1] = g[0] = g[1] = b = 0;
    for(int i = 0; i < n; i++) {
        add(i);
    }
    print();
    while(q--) {
        int i;
        char c;
        cin >> i >> c;
        i--;
        del(i);
        s[i] = c;
        add(i);
        print();
    }
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int testNum = 1;
    //cin >> testNum;
    for(int i = 1; i <= testNum; i++) {
        //cout << "Case #" << i << ": ";
        solve();
    }
    return 0;
}