d.cpp

#include <bits/stdc++.h>
const int mod = (int)1e9+7;
int pow(int a, int n) {
    int res = 1;
    while (n > 0) {
        if (n % 2 == 1) {
            res = int(1LL * res * a % mod);
        }
        a = int(1LL * a * a % mod);
        n /= 2;
    }
    return res;
}
int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(0);
    // input:
    int n;
    std::cin >> n;
    std::string s;
    std::cin >> s;
    // counting letters:
    std::vector<int> count(256);
    for (int i = 0; i < n; i++) {
        count[s[i]]++;
    }
    // calculating factorials:
    std::vector<int> factorial(1+n);
    factorial[0] = 1;
    for (int i = 1; i <= n; i++) {
        factorial[i] = int(1LL * factorial[i-1] * i % mod);
    }
    // calculating inverse factorials in linear time:
    // 1/n! = pow(n!, mod-2)
    std::vector<int> inverseFactorial(1+n);
    inverseFactorial[n] = pow(factorial[n], mod-2);
    // 1/(n-1)! = n * (1/n!)
    for (int i = n-1; i >= 0; i--) {
        inverseFactorial[i] = int(1LL * inverseFactorial[i+1] * (i+1) % mod);
    }
    // getting answer:
    int answ = factorial[n];
    for (char c = 'a'; c <= 'z'; c++) {
        answ = int(1LL * answ * inverseFactorial[count[(int)c]] % mod);
    }
    std::cout << answ << std::endl;
    // answering on queries:
    int q; std::cin >> q;
    while (q--) {
        int pos; char newChar;
        std::cin >> pos >> newChar;
        pos--;
        char oldChar = s[pos];
        s[pos] = newChar;
        answ = int(1LL * answ * factorial[count[(int)oldChar]] % mod);
        answ = int(1LL * answ * factorial[count[(int)newChar]] % mod);
        count[oldChar]--;
        count[newChar]++;
        answ = int(1LL * answ * inverseFactorial[count[(int)oldChar]] % mod);
        answ = int(1LL * answ * inverseFactorial[count[(int)newChar]] % mod);
        std::cout << answ << "\n";
    }
    return 0;
}