P1591 阶乘数码

题目传送门

#include <bits/stdc++.h>

using namespace std;

//高精度乘法模板
vector<int> mul(vector<int> &A, int b) {
    vector<int> C;
    int t = 0;
    for (int i = 0; i < A.size() || t; i++) {
        if (i < A.size()) t += A[i] * b;
        C.push_back(t % 10);
        t /= 10;
    }
    while (C.size() > 1 && C.back() == 0) C.pop_back();
    return C;
}

int main() {
    int t;
    cin >> t;
    for (int i = 1; i <= t; i++) {
        int n, a;
        cin >> n >> a;

        vector<int> A;
        int cnt = 0;
        //倒着放的噢~
        A.push_back(1);
        for (int j = 2; j <= n; j++) A = mul(A, j);

        //这个求a出现的次数，就是一个暴力求全部！
        for (int j = 0; j < A.size(); j++)
            if (A[j] == a) cnt++;
        cout << cnt << endl;
    }
    return 0;
}