Misha hacked the Codeforces site. Then he decided to let all the users change their handles. A user can now change his handle any number of times. But each new handle must not be equal to any handle that is already used or that was used at some point.
Misha has a list of handle change requests. After completing the requests he wants to understand the relation between the original and the new handles of the users. Help him to do that.
InputThe first line contains integer q (1 ≤ q ≤ 1000), the number of handle change requests.
Next q lines contain the descriptions of the requests, one per line.
Each query consists of two non-empty strings old and new, separated by a space. The strings consist of lowercase and uppercase Latin letters and digits. Strings old and new are distinct. The lengths of the strings do not exceed 20.
The requests are given chronologically. In other words, by the moment of a query there is a single person with handle old, and handle new is not used and has not been used by anyone.
In the first line output the integer n — the number of users that changed their handles at least once.
In the next n lines print the mapping between the old and the new handles of the users. Each of them must contain two strings, old and new, separated by a space, meaning that before the user had handle old, and after all the requests are completed, his handle is new. You may output lines in any order.
Each user who changes the handle must occur exactly once in this description.
5 Misha ILoveCodeforces Vasya Petrov Petrov VasyaPetrov123 ILoveCodeforces MikeMirzayanov Petya Ivanov
3 Petya Ivanov Misha MikeMirzayanov Vasya VasyaPetrov123
题目大意：输入q项更改用户名的请求，第一个字符串为旧用户名，第二个字符串为新用户名。Misha想要知道最新的用户名与最初始的用户名所对应的关系，输出最初始的用户名与最新的用户名。
该题主要是一个映射关系，所以考虑用map来求解，使用map时，以新用户名作为键值，每次将新的用户名对插入map里时，判断旧的用户名是否是map中的键值，若是则说明旧的用户名也是经过修改的用户名，通过map[new]=map[old]语句即可将最新的用户名与原始用户名关联起来。
代码：
#include<stdio.h>
#include<iostream>
#include<string>
#include<map>
#include<algorithm>
using namespace std;
int main(void) {
int q;
map<string, string>mp;
string olds, news;
scanf("%d", &q);
while (q--) {
cin >> olds >> news;
if (!mp.count(olds)) mp[news] = olds;
else {
mp[news] = mp[olds];
mp.erase(olds);
}
}
cout << mp.size() << endl;
for (map<string, string>::iterator it = mp.begin(); it != mp.end(); it++)
cout << it->second <<' '<<it->first<< endl;
return 0;
}