学步园

题目：求最大的集合的元素个数。

分析：并查集。

注意：输入使用while( scanf("%d",&T) != EOF )会TLE。

#include <stdio.h>
#include <stdlib.h>

//union_set_begin
int sets[ 30001 ];
int rank[ 30001 ];
int size[ 30001 ];

void union_set( int n )
{
	for ( int i = 0 ; i <= n ; ++ i ) {
		rank[i] = 0;
		size[i] = 1;
		sets[i] = i;
	}
}

int Find( int a )
{
	if ( a != sets[a] )
		sets[a] = Find( sets[a] );
	return sets[a];
}

int Union( int a, int b )
{
	if ( rank[a] > rank[b] ) {
		sets[b] = a;
		size[a] += size[b];
	}else {
		sets[a] = b;
		size[b] += size[a];
		if ( rank[a] == rank[b] )
			rank[b] ++;
	}
}
//union_set_end

int x[500001];
int y[500001];

int main()
{
	int T,N,M,a,b; 
	scanf("%d",&T);
	while ( T -- ) {
		scanf("%d%d",&N,&M);
		union_set( N );
		for ( int i = 1 ; i <= M ; ++ i )
			scanf("%d%d",&x[i],&y[i]);
		
		for ( int i = 1 ; i <= M ; ++ i ) {
			a = Find( x[i] );
			b = Find( y[i] );
			if ( a != b )
				Union( a, b ); 
		}
		int max = 1;
		for ( int i = 1 ; i <= N ; ++ i )
			if ( max < size[i] )
				max = size[i];
		printf("%d\n",max);
	}
	return 0;
}