题解 | 添加逗号

#include <iostream>
using namespace std;
#include<string>
#include<algorithm>
int main() {
   string s,s1;
   cin>>s;//980364535
   reverse(s.begin(),s.end());//535463089
   for(int i=1;i<=s.size();i++){
    s1+=s[i-1];
        if(i%3==0&&i!=s.size()){
           s1.append(",");
        }    
   }
   reverse(s1.begin(),s1.end());
   cout<<s1;
}
// 64 位输出请用 printf("%lld")