CF501B STL

有n个修改操作，一些人会把原本的handle做修改，最后问有哪些handle被修改并输出这些handle的最终版本

用map记录修改映射，vector记录最初的handle

#include<bits/stdc++.h>#define PB push_backusing namespace std;map<string, string> mp;vector<string> vec;int main(){    int n;    string from, to;    cin >> n;    for (int i = 1; i <= n; i++){        cin >> from >> to;        if (mp.find(from) == mp.end()){            mp[from] = to;            mp[to] = from;            vec.PB(from);        }        else{            mp[mp[from]] = to;            mp[to] = mp[from];        }    }    //sort(vec.begin(), vec.end());    int sz = vec.size();    cout << sz << endl;    for (int i = 0; i < sz; i++)        cout << vec[i] << " " << mp[vec[i]] << endl;    return 0;}