hdu 1232

# include <stdio.h>
# include <string.h>
int node[1005];
int getfather(int a)
{
	return (node[a]==a)?a:(node[a]=getfather(node[a]));
}
int main ()

{
	int m,n,i;
	int a,b,mark;
	while(scanf("%d",&m)!=EOF)
	{
		if(m==0)
			break;
		scanf("%d",&n);
		for(i=0;i<=m;i++)
		{node[i]=i;}
		for(i=1;i<=n;i++)
		{
			scanf("%d%d",&a,&b);
			int t1 = getfather(a);
			int t2 = getfather(b);
			node[a]=t1;
			node[b]=t2;
			if(t1!=t2)
			{
				node[t2]=t1;
			}
		}
		mark=0;
		for(i=1;i<=m;i++)
			if(node[i]==i)
				mark++;
	
		printf("%d\n",mark-1);
	}
	return 0;
}

并查集的问题 注意 node[t2]=t1; 这样才是把两棵树合并成一棵树