上个月的水题，瞪了几天没调出来。

#include <bits/stdc++.h>
// #define int long long
#define endl '\n'
using namespace std;
const int N = 1e5+5;

int q,n;
string s;
char c;
int cnt,x;

signed main(){
    ios::sync_with_stdio(0);
    cin.tie(NULL);
    
    cin >> n >> q >> s;
    
    int si = s.size();
    s = '-' + s;
    for(int i = 1; i < si-1; i++){
        if(s[i] != 'a' || s[i+1] != 'b' || s[i+2] != 'c')
            continue;
        cnt++;
    }
    
    while(q--){
        cin >> x >> c;
        if(s[x] == c){
            cout << cnt << endl;
            continue;
        }
        
        if(x < si-1 && s[x] == 'a' && s[x+1] == 'b' && s[x+2] == 'c'
          || x > 1 && x < si && s[x-1] == 'a' && s[x] == 'b' && s[x+1] == 'c'
          || x > 2 && s[x-2] == 'a' && s[x-1] == 'b' && s[x] == 'c'){
            cnt--,s[x] = c;;
            cout << cnt << endl;
            continue;
        }
        
        if(c == 'a' && x < si-1 && s[x+1] == 'b' && s[x+2] == 'c') cnt++;
        else if(c == 'b' && x > 1 && x < si && s[x-1] == 'a' && s[x+1] == 'c') cnt++;
        else if(c == 'c' && x > 2 && s[x-2] == 'a' && s[x-1] == 'b') cnt++;
        
        s[x] = c;
        cout << cnt << endl;
        // cout << s << endl;
    }
    return 0;
}