CodeForces 501B - Misha and Changing Handles

有N个改名的动作，输出改完名的最终结果。

拿map做映射

 #include <iostream>
 #include <map>
 #include <string>
 using namespace std;
 map<string,string> mp;
 map<string,int> vis;
 int n;
 string s1,s2;
 int main()
 {
     cin>>n;
     map<string,string>::iterator it;
     for(int i=;i<=n;i++)
     {
         cin>>s1>>s2;
         if(!vis[s1]&&!vis[s2])
         {
             vis[s1]=; vis[s2]=; mp[s1]=s2;
         }
         else if(vis[s1]&&!vis[s2])
         {
             vis[s2]=;
             for(it=mp.begin();it!=mp.end();it++)
             {
                 if(it->second==s1)
                 {
                     it->second=s2; break;
                 }
             }
         }
     }
     cout<<mp.size()<<endl;
     for(it=mp.begin();it!=mp.end();it++)
     {
         cout<<it->first<<" "<<it->second<<endl;
     }
 }