求助全WA

#include <iostream>
#include <algorithm>
#include <string>
#include <cstdio>
#include <vector>

using namespace std;
typedef long long LL;
int k,n,y,ans;

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()
{

    string a;
    vector<int> A,B;
    cin >> n;
    while(n--)
    {
    cin >> a;
    cin >> k;
    for(int i=a.size()-1,j=1;i>=0;i--,j*=10)
    { 
        A.push_back(a[i]-'0');
        y=(a[i]-'0')*j;
    }
    for(int i=y-1;i>=1;i--)
    {
        A=mul(A,i);
    }

    for(auto i:A)
    if(i==k)ans++;
    printf("%d\n",ans);
    ans=0;
    A.clear();
    }

}