F - Firetrucks Are Red Kattis - firetrucksarered（并查集加路径压缩）

Lily is fascinated by numbers. She believes the whole world revolves around them, and that everything is connected by numbers. Her friends, Alice, Bob, Charlie and Diane, are not convinced. But she gives them an example:
Alice lives in house number 25 on her street, but that is exactly Bob’s age. Bob is born on June 4th, and Charlie was his parents’ fourth child. Finally, Diane has five fingers on her left hand, which happens to be the same as the number of toes that Bob has on his right foot!
This shows that her friends are all connected—either directly or indirectly—by numbers. But she still has to convince her family as well as her coworkers.

Given a group of n individuals, and a set of numbers that describe each individual, help Lily come up with a proof that shows that everyone in this group is either directly or indirectly connected by numbers, or determine that this is not possible.

Input
The input consists of:

One line with an integer n (2≤n≤2⋅105), the number of individuals in the group. The individuals are numbered from 1 to n.

n lines, describing the individuals in the group.

The ith such line starts with an integer mi (1≤mi≤2⋅105), the number of numbers that describe individual i.

The remainder of the line has mi distinct integers di,1,…,di,mi (1≤di,j≤109 for each j), the set of numbers that describe individual i.

It is guaranteed that the sum over all mi is at most 2⋅105.

Output
Output a proof in the form of n−1 lines, each of which contains three integers p, q and r, where p and q are distinct individuals that are both described by the number r. Using only these relations, it must be possible to show that any pair of individuals in the group are connected either directly or indirectly.

If no such proof exists, output “impossible”. If there are multiple proofs, you may output any one of them.

思路：并查集加路径压缩
代码：

#include <algorithm>
#include <stdio.h>
#include <cstring>
#include <deque>
#include <list>
#include <map>
#include <iostream>
#include <istream>
#include <queue>
#include <stack>
#include <vector>
using namespace std;
#define INF 0x3f3f3f3f
#define Max 1000001
map<int,int>vis;
int parent[200001];
int n;
int book1[200001];
int book2[200001];
int book3[200001];
int ans=0;
void init()
{
    for(int i=1;i<=n;i++)
    {
        parent[i]=i;
    }
}
int Find(int x)
{
    if(parent[x]!=x)
        parent[x]=Find(parent[x]);
    return parent[x];
}

void Merge(int x,int y,int key)
{
    if(Find(x)!=Find(y))
    {
        parent[Find(y)]=Find(x);
        book1[ans]=x;
        book2[ans]=y;
        book3[ans++]=key;
    }
    return;
}
int main()
{
    cin>>n;
    init();
    for(int i=1;i<=n;i++)
    {
        int m;
        cin>>m;
        for(int j=0;j<m;j++)
        {
            int key;
            cin>>key;
            if(vis[key]==0)
            {
                vis[key]=i;
            }
            else
            {
                Merge(vis[key],i,key);
                vis[key]=i;
            }
        }
    }
    if(ans==n-1)
    {
        for(int i=0;i<ans;i++)
            cout<<book1[i]<<" "<<book2[i]<<" "<<book3[i]<<endl;
    }
    else
    {
        cout<<"impossible"<<endl;
    }
    return 0;
}