stl set使用

#include <set>
#include <iostream>
#include <stdio.h>
using namespace std;
int main()
{
	int n,m;
	while(scanf("%d%d",&n,&m)!=EOF && n!=-1 && m!=-1)
	{
		set <int > R_num;
		set <int > B_num;
		for(int i=1; i<=m; i++)
		{
			int x,y;
			scanf("%d%d",&x,&y);
			if(i%2!=0)
			{
				R_num.insert(x);
				R_num.insert(y);
				if(B_num.find(x)!=B_num.end() )
					B_num.erase(x);
				if(B_num.find(y)!=B_num.end() )
					B_num.erase(y);
			}
			else
			{
				B_num.insert(x);
				B_num.insert(y);
				if(R_num.find(x)!=R_num.end() )
					R_num.erase(x);
				if(R_num.find(y)!=R_num.end() )
					R_num.erase(y);
			}
		}
		if(B_num.size()==n)
			printf("YES\n");
		else
			printf("NO\n");
		set<int >::iterator iter;
		for(iter=R_num.begin(); iter!=R_num.end(); iter++)
			cout << *iter << endl;
	}
	return 0;
}

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