我一次性AC这道题，用时20分钟。

#include<iostream>
#include<sstream>
using namespace std;
int main()
{
//  freopen("xxx.in","r",stdin);
//  freopen("yyy.out","w",stdout);
    string s,n1,n2="";
    stringstream ss; 
    getline(cin,s);
    ss<<s;
    while(ss>>n1)
    {
        n2=' '+n1+n2;
    }
    n2.erase(0,1);
    cout << n2;
//  fclose(stdin);
//  fclose(stdout);
    return 0;
 }