C++ 代码
#include<bits/stdc++.h>
using namespace std;
map<string, string> f;
int main()
{
int n; cin >> n;
while (n--)
{
string s1, s2; cin >> s1 >> s2;
if (f.count(s1) == 0)f.insert({ s2, s1 });
else
{
f.emplace(s2, f.at(s1));
f.erase(s1);
}
}
cout << f.size() << endl;
for (map<string, string>::iterator it = f.begin(); it != f.end(); it++)
{
cout << it->second << ' ' << it->first << "\n";
}
}