CF 501B Misha and Changing Handles(map+技巧)

题意：A有别名B，B有别名C......求实际上有多少个人，并输出最后一个别名

Input

5
Misha ILoveCodeforces
Vasya Petrov
Petrov VasyaPetrov123
ILoveCodeforces MikeMirzayanov
Petya Ivanov

Output

3
Petya Ivanov
Misha MikeMirzayanov
Vasya VasyaPetrov123

思路：构造MAP。（B,A) .(C,B).就能直接构造出数对（C,A),运用mp[s2] = mp[s1];进行转换

 

#include <iostream>
#include <cstdio>
#include <set>
#include <map>
#include <string>

using namespace std;

int n;
string s1,s2;
map<string,string>mp;

int main()
{
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    cin>>n;
    for(int i=0;i<n;i++)
    {
        cin>>s1>>s2;
        if(mp.count(s1)==0) mp[s1]=s1;
        mp[s2]=mp[s1];
        mp.erase(s1);
    }
    cout<<mp.size()<<endl;
    for(map<string,string>::iterator it=mp.begin();it!=mp.end();it++)
    {
        cout<<(*it).second<<" "<<(*it).first<<endl;
    }
    return 0;
}