K - rochambau (joint search, enumeration)

N children are playing Rochambeau (scissors-rock-cloth) game with you. One of them is the judge. The rest children are divided into three groups (it is possible that some group is empty). You don’t know who is the judge, or how the children are grouped. Then the children start playing Rochambeau game for M rounds. Each round two children are arbitrarily selected to play Rochambeau for one once, and you will be told the outcome while not knowing which gesture the children presented. It is known that the children in the same group would present the same gesture (hence, two children in the same group always get draw when playing) and different groups for different gestures. The judge would present gesture randomly each time, hence no one knows what gesture the judge would present. Can you guess who is the judge after after the game ends? If you can, after how many rounds can you find out the judge at the earliest?

Input
Input contains multiple test cases. Each test case starts with two integers N and M (1 ≤ N ≤ 500, 0 ≤ M ≤ 2,000) in one line, which are the number of children and the number of rounds. Following are M lines, each line contains two integers in [0, N) separated by one symbol. The two integers are the IDs of the two children selected to play Rochambeau for this round. The symbol may be “=”, “>” or “<”, referring to a draw, that first child wins and that second child wins respectively.

Output
There is only one line for each test case. If the judge can be found, print the ID of the judge, and the least number of rounds after which the judge can be uniquely determined. If the judge can not be found, or the outcomes of the M rounds of game are inconsistent, print the corresponding message.

Sample Input
3 3
0<1
1<2
2<0
3 5
0<1
0>1
1<2
1>2
0<2
4 4
0<1
0>1
2<3
2>3
1 0
Sample Output
Can not determine
Player 1 can be determined to be the judge after 4 lines
Impossible
Player 0 can be determined to be the judge after 0 lines
The question ：
Learn from the boss blog

#include <cstdio>
#include <cmath>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <map> 
#include <stack>
using namespace std;
using namespace std;
const int maxn=100006;
int pre[10005],rank[10005];
int n,m; 
struct node{
    
	int v,u,op;
}a[22222];
int find(int x)
{
    
	if(pre[x]==x)
	return x;
	
		int t=pre[x];
		pre[x]=find(t);
		rank[x]=(rank[x]+rank[t])%3;
		return pre[x];
	
}
void unit()
{
    
	for(int i=0;i<=n;i++)
	{
    
			pre[i]=i;
			rank[i]=0;// I am the same as myself  
	}

}
bool judge(int v,int u,int op)
{
    
	int fx=find(v);
	int fy=find(u);
	if(fx==fy)
	{
    
		return ((rank[v]-op+3)%3!=rank[u]);
	}
	else
	{
    
		pre[fx]=fy;
		rank[fx]=(rank[u]+op-rank[v]+3)%3;
		return 0;
	}
}
int main()
{
    
	while(cin>>n>>m)
	{
    
		char c;
		
		for(int i=1;i<=m;i++)// from 1 Start , There are no rows 0 
		{
    
			cin>>a[i].v>>c>>a[i].u;
			if(c=='=')
			a[i].op=0;
			if(c=='>')
			a[i].op=2;
		    if(c=='<')
			a[i].op=1;
		}
		int line=0;// Determine the subscript of the referee  
		int num=0;// Number of referees found  
		int temp;// The referee's subscript  
		for(int i=0;i<n;i++)
		{
    
			unit();
			int flag=1;
			for(int j=1;j<=m;j++)
			{
    
				int v=a[j].v,u=a[j].u,op=a[j].op;
				if(a[j].v==i||a[j].u==i)// enumeration , Suppose the referee  
				continue;
				if(judge(v,u,op))// There are contradictions , That is, the assumption is not true ,i Not the referee . 
				{
    
					flag=0;
		            line=max(line,j);
		            break;
				}
			}
			if(flag)// Suppose it is true .i It's the referee  
			{
    
				
				temp=i;
				num++; 
			}
		}
		if(num==0)// No referee  
		{
    
			cout<<"Impossible"<<endl;
		}
		else if(num>1)// There are multiple referees  
		cout<<"Can not determine"<<endl;
		else
		cout<<"Player "<<temp<<" can be determined to be the judge after "<<line<<" lines"<<endl;
	}
	return 0; 
}