Misha and Changing Handles CodeForces

 

Misha and Changing Handles

CodeForces - 501B

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.

Input

The 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. Stringsold andnew are distinct. The lengths of the strings do not exceed20.

The requests are given chronologically. In other words, by the moment of a query there is a single person with handleold, and handlenew is not used and has not been used by anyone.

Output

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 andnew, separated by a space, meaning that before the user had handleold, and after all the requests are completed, his handle isnew. You may output lines in any order.

Each user who changes the handle must occur exactly once in this description.

Example

Input

5Misha ILoveCodeforcesVasya PetrovPetrov VasyaPetrov123ILoveCodeforces MikeMirzayanovPetya Ivanov

Output

3Petya IvanovMisha MikeMirzayanovVasya VasyaPetrov123

思路：使用map映射，前面的key值储存最新的改变的名字，第二个值则储存最初的名字，也可称为父亲名字

每次输入的时候，前一个作为old名字，如果map中key值没有这个说明是第一次该，创建一个指向自己，然后新的名字映射老名字，最后删去老名字，如果有，说明这个是经过多次修改后得到的目前名字，现在再把这个名字改成新的，操作相同，不需要创建新的映射

code：

#include <iostream>#include <cstdio>#include <map>#include <string>using namespace std;int main(){int n;while(~scanf("%d",&n)){string a,b;map<string,string>mp;//建立一个map映射 int i;for(i = 0; i < n; i++){cin >> a >> b;if(!mp.count(a)){//如果old名字不存在，说明这是第一次出现 mp[a] = a;//建立一个指向自己的映射 }mp[b] = mp[a];//new指向old的映射mp.erase(a); }map<string,string>::iterator it;cout << mp.size() << endl;for(it = mp.begin(); it != mp.end(); it++)   cout << it->second << ' ' << it->first << endl;}return 0;}