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
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
#include <iostream>

const int64_t MOD = 1000000007;

const int M[5][5] = {
    {1, 4, 0, 0, 0},
    {4, 0, 1, 1, 1},
    {0, 1, 2, 4, 4},
    {0, 1, 4, 3, 4},
    {0, 1, 4, 4, 4},
};

const int64_t A[4][2] = {
    {1, 0},
    {0, 1},
    {1, 1},
    {0, 0}
};

int AA(char c) {
    switch (c) {
        case 'Z': return 0;
        case 'C': return 1;
        case 'N': return 2;
    }
    return 3;
}

struct V {
    int64_t x[5];

    static V make(const int64_t a[2], const int64_t b[2]) {
        V v;
        // std::clog << a[0] << " " << a[1] << " | "  << b[0] << " " << b[1] << std::endl;
        v.x[0] = a[0]*b[0]%MOD;
        v.x[1] = a[1]*b[1]%MOD;
        v.x[2] = a[0]*b[1]%MOD;
        v.x[3] = a[1]*b[0]%MOD;
        v.x[4] = 0;
        return v;
    }

    V operator+(const V& w) const {
        const V& v = *this;
        if (w.x[0] == -1) return v;
        if (v.x[0] == -1) return w;
        V u;
        for (int i=0;i<5;++i)
            u.x[i] = 0;
        for (int i=0;i<5;++i) {
            for (int j=0;j<5;++j) {
                int64_t& xx = u.x[M[i][j]];
                xx = (xx + v.x[i]*w.x[j]) % MOD;
            }
        }
        return u;
    }

    int64_t C() const {
        return (x[0]+x[1])%MOD;
    }

    int64_t C(char c) const {
        if (c=='Z')
            return (x[1]+x[3]+x[4])%MOD;
        else if (c=='C')
            return (x[0]+x[2]+x[4])%MOD;
        else if (c=='N')
            return (C('Z')+C('C'))%MOD;
        else return 0;
    }
};

std::ostream& operator<<(std::ostream& out, V v) {
    out << "{" << v.x[0] << ", " << v.x[1] << ", " << v.x[2] << ", " << v.x[3] << ", " << v.x[4] << "}";
    return out;
}

const int MAX = 1<<18;
// const int MAX = 1<<4;
V D[MAX];
std::string S;
int n,q;

V make(char a, char b) {
    return V::make(A[AA(a)], A[AA(b)]);
}

void init() {
    for (int i=0;i<MAX;i++) D[i].x[0] = -1;
    for (int i=0;i+1<n;i+=2) {
        D[MAX/2+i/2] = make(S[i], S[i+1]);
        // std::clog << MAX/2+i/2 << " :: " << D[MAX/2+i/2]<<std::endl;
    }
    for (int i=MAX/2-1;i>0;--i) {
        D[i] = D[2*i]+D[2*i+1];
        // std::clog << i << " :: " << D[i]<<std::endl;
    }
}

void update(int i) {
    i = i/2*2;
    D[MAX/2+i/2] = make(S[i], S[i+1]);
    i = MAX/2+i/2;
    // std::clog << i << " :: " << D[i]<<std::endl;

    while (i>1) {
        i/=2;
        D[i] = D[2*i]+D[2*i+1];
        // std::clog << i << " :: " << D[i]<<std::endl;
    }
    // init();
}


/*
5
1 1 | 1 0
8 :: {1, 0, 0, 1, 0}
1 1 | 0 1
9 :: {0, 1, 1, 0, 0}
7 :: {-1, 0, 0, 0, 0}
6 :: {-1, 0, 0, 0, 0}
5 :: {-1, 0, 0, 0, 0}
4 :: {1, 1, 0, 0, 2}
3 :: {-1, 0, 0, 0, 0}
2 :: {1, 1, 0, 0, 2}
1 :: {1, 1, 0, 0, 2}
*/
int64_t sol() {
    if (n%2 == 0) return D[1].C();
    else return D[1].C(S[n-1]);
}

int main() {
    std::ios_base::sync_with_stdio(0);
    std::cin >> n >> q;
    std::cin >> S;
    init();
    std::cout << sol() << "\n";
    for (int i=0;i<q;++i) {
        int k;
        char c;
        std::cin >> k >> c;
        --k;
        S[k] = c;
        if (n%2==0 || k!=n-1)
            update(k);
        std::cout << sol() << "\n";
    }
    return 0;
}