高精度AxB

洛谷1303

#include<iostream>
using namespace std;
const int N = 50000;
int arr[2*N];
int aa[N];
int bb[N];
int main(){
    string a,b;
    cin>>a>>b;
    for(int i = a.length()-1;i>=0;i--){
        
        aa[a.length()-i-1] = a.at(i)-'0';
    }
    for(int i = b.length()-1;i>=0;i--){
        bb[b.length()-i-1] = b.at(i)-'0';
    }
    for(int i  = 0 ;i<a.length();i++){
        for(int j=0;j<b.length();j++){
            arr[i+j] +=bb[j]*aa[i]; 
        }
    }
    int len = a.length()+b.length();
     for(int i = 0;i<=len;i++){
        arr[i+1] += arr[i]/10;
        arr[i]%=10;
    }
    while(!arr[len]){
        len--;
    }
    if(len<0)
    cout<<0;else
    for(int i = len;i>=0;i--)
    cout<<arr[i];
}