题解 | #N的阶乘#

#include <bits/stdc++.h>

using namespace std;

vector<int> multiply(vector<int>& a, int num){
    int carry = 0;
    vector<int> res;
    for(int i=0;i<a.size();i++){
        carry = a[i]*num + carry;
        res.push_back(carry%10);
        carry /= 10;
    }
    while(carry){
        res.push_back(carry%10);
        carry /= 10;
    }
    return res;
}

int main()
{
    int n;
    while(cin >> n)
    {
        vector<int> ans;
        ans.push_back(1);
        for(int i=n;i>1;i--){
            ans = multiply(ans, i);
        }
        for(int i=ans.size()-1;i>=0;i--){
            cout<<ans[i];
        }
        cout<<endl;
    }
    return 0;
}