不太明白为什么会全wa，0分求调，样例明明能过啊，怎么会0分

#define  _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <cstdio>
#include <cstring>
#include <queue>
#include <cstdlib>
#include <algorithm>
#include <list>
#include <string>
#include <cmath>
#include <bitset>

vector<long long >mul(vector<long long >A, vector<long long >B) {
    vector<long long >C(A.size() + B.size());
    for (int i = 0; i < A.size(); i++) {
        for (int j = 0; j < B.size(); j++) {
            C[i + j] += A[i] * B[j];
            C[i + j + 1] += C[i + j] / 10;
            C[i + j] %= 10;
        }
    }
    while (C.size() > 0 && C.back() == 0)C.pop_back();
    return C;
}
int main() {
    int t; cin >> t;
    while (t--) {
        int a, b; cin >> a >> b;
        vector<long long >B(1);
        vector<long long >A(1);
        A[0] = 1; long long sum = 0;
        for (int i = 1; i <= a; i++) {
            B[0] = i;
            A = mul(A, B);
        }
        for (auto a : A) {
            if (a == b) {
                sum++;
            }
        }
        cout << sum << endl;
    }

    return 0;
}