题解 | 数字阶梯求和

#include<iostream>
#include<string>
#include<algorithm>
using namespace std;
string addstring(string a,string b){
    while(a.size()<b.size()){
        a='0'+a;
    }
    while(b.size()<a.size()){
        b='0'+b;
    }
    string res;
    int carry=0;
    for(int i=a.size()-1;i>=0;i--){
        int num=a[i]-'0'+b[i]-'0'+carry;
        carry=num/10;
        res+=num%10+'0';
    }
    if(carry!=0)    res+=carry+'0';
    reverse(res.begin(),res.end());
    return res;
}

int main(){
    int a;
    while(cin>>a){
        int n;
        cin>>n;
        string res=to_string(a);
        string count="0";
        for(int i=1;i<=n;i++){
            string temp=res;
            for(int j=2;j<=i;j++){
                temp+=res;
            }
            count=addstring(count,temp);
        }
        cout<<count<<endl;
    }
}