多种解法 题解 100% AC

1. 高精度：

#include<bits/stdc++.h>
using namespace std;
int a[10010],b[10010],c[10010];
string mul(string s1,string s2){
	memset(a,0,sizeof(a)),memset(b,0,sizeof(b)),memset(c,0,sizeof(c));
	a[0]=s1.size(),b[0]=s2.size();
	for(int i=1;i<=a[0];i++)a[i]=s1[a[0]-i]-'0';
	for(int i=1;i<=b[0];i++)b[i]=s2[b[0]-i]-'0';
	for(int i=1;i<=a[0];i++)for(int j=1;j<=b[0];j++)c[i+j-1]+=a[i]*b[j];
	c[0]=a[0]+b[0];
	for(int i=1;i<=c[0];i++){
		c[i+1]+=c[i]/10;
		c[i]=c[i]%10;
	}
	while(c[c[0]]==0&&c[0]>1)c[0]--;
	string ans;
	for(int i=c[0];i>=1;i--)ans+=c[i]+'0';
	return ans;
}
int main(){
	int n;
	cin>>n;
	while(n--){
		int x,cnt=0;
		char s;
        string ans="1";
		cin>>x>>s;
		for(int i=1;i<=x;i++)ans=mul(ans,to_string(i));
		for(int i=0;i<ans.size();i++)if(ans[i]==s)cnt++;
		cout<<cnt<<endl;
	}
	return 0;
}

2. 预处理：

#include <bits/stdc++.h>
using namespace std;
vector<vector<int>> factorial(1001);
void init_factorials() {
    factorial[0] = {1};
    factorial[1] = {1};
    for(int i = 2; i <= 1000; ++i) {
        vector<int> current = factorial[i-1];
        int carry = 0;
        for(int &digit : current) {
            int product = digit * i + carry;
            digit = product % 10;
            carry = product / 10;
        }
        while(carry) {
            current.push_back(carry % 10);
            carry /= 10;
        }
        factorial[i] = current;
    }
}
int count_digit(int n, int target) {
    int count = 0;
    for(int digit : factorial[n]) {
        if(digit == target) {
            ++count;
        }
    }
    return count;
}
int main() {
    init_factorials();
    int t;
    cin >> t;
    while(t--) {
        int n, a;
        cin >> n >> a;
        cout << count_digit(n, a) << endl;
    }
    return 0;
}