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
#include <bits/stdc++.h>

using namespace std;

#define ll long long

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;

typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;

typedef pair<int,int> ii;

template<class t> using vc=vector<t>;
template<class t> using vvc=vc<vc<t>>;

const int MOD = 998244353;

ll read(){
    ll i;
    cin>>i;
    return i;
}

vi readvi(int n,int off=0,int shift=0){
    vi v(n+shift);
    rep(i,shift)v[i]=0;
    rep(i,n)v[i+shift]=read()+off;
    return v;
}

void YesNo(bool condition, bool do_exit=true) {
    if (condition)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
    if (do_exit)
        exit(0);
}

int main(void ) {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    int n,q;
    cin >> n >> q;

    string s;

    cin >> s;
    n = s.length();

    rep(_,q+1) {

        vvvi dp(3, vvi(2, vi(n)));

        dp[0][0][0] = 1; // nie wzięte a+, nie było powt.
        dp[1][0][0] = 0; // nie wzięte,ab+ nie było powt.
        dp[2][0][0] = 1; //     wzięte,    nie było powt.
        dp[0][1][0] = 0; // nie wzięte,a+   było powt.
        dp[1][1][0] = 0; // nie wzięte,ab+  było powt.
        dp[2][1][0] = 0; //     wzięte,     było powt.

        vi prev[2] = {vi(n, -1), vi(n, -1)};
        int last[2] = {-1, -1};
        last[s[0] - 'a'] = 0;

        rng(i, 1, n) {
            rep(j, 2)prev[j][i] = last[j];
            last[s[i] - 'a'] = i;

            rep(j, 2)dp[2][j][i] = (dp[2][j][i - 1] + (s[i] != s[i - 1]) * dp[0][j][i - 1]) % MOD;
            dp[0][0][i] = ((s[i] == s[i - 1]) * dp[0][0][i - 1] + (s[i] != s[i - 1]) * dp[2][0][i - 1]) % MOD;
            dp[0][1][i] = (((s[i] == s[i - 1]) * dp[0][1][i - 1] + dp[2][1][i - 1]) % MOD + dp[2][0][i - 1] * (s[i] == s[i - 1])) % MOD;
            dp[1][0][i] = (s[i] == s[i - 1]) * dp[1][0][i - 1];
            dp[1][1][i] = (((s[i] == s[i - 1]) * dp[1][1][i - 1] +
                          (s[i] != s[i - 1]) * ((prev[s[i] - 'a'][i] >= 0) * dp[0][0][i - 1]) % MOD + dp[0][1][i - 1])) % MOD;

            /*
            cout << "i=" << i << " " << s.substr(0, i+1) << endl;
            rep(j,3)
                rep(k,2)
                  cout << "dp["<<j <<k<<"]= " << dp[j][k][i] << endl;
            */
        }

        int res = 0;
        rep(i, n) {
            res += dp[2][1][i];
            res %= MOD;
            res += (i > 0 and s[i] == s[i - 1]) * dp[2][0][i - 1];
            res %= MOD;
            res += (i > 0 and s[i] != s[i - 1] and prev[s[i] - 'a'][i - 1] >= 0) * dp[2][0][prev[s[i] - 'a'][i - 1]];
            res %= MOD;
            //cout << dp[2][1][i] << " " << (i > 0 and s[i] == s[i - 1]) * dp[2][0][i - 1]  << " " << (i > 0 and s[i] != s[i - 1] and prev[s[i]-'a'][i-1] >= 0) * dp[2][0][prev[s[i]-'a'][i-1]] << endl;
        }
        cout << res << endl;

        if (_ < q) {
            int i; char c;
            cin >> i >> c;
            s[i] = c;
        }

    }

    return 0;
}