【POJ】1655 Balancing Act 树的重心

传送门：【POJ】1655 Balancing Act

题目分析：树的重心模板题。

代码如下：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std ;

typedef long long LL ;

#define travel( e , H , u ) for ( Edge* e = H[u] ; e ; e = e -> next )
#define rep( i , a , b ) for ( int i = ( a ) ; i <  ( b ) ; ++ i )
#define rev( i , a , b ) for ( int i = ( a ) ; i >= ( b ) ; -- i )
#define FOR( i , a , b ) for ( int i = ( a ) ; i <= ( b ) ; ++ i )
#define clr( a , x ) memset ( a , x , sizeof a )
#define cpy( a , x ) memcpy ( a , x , sizeof a )
#define F( i ) ( ( ( i ) - 1 ) % n + 1 )

const int MAXN = 20005 ;
const int MAXE = 40005 ;

struct Edge {
	int v ;
	Edge* next ;
} E[MAXE] , *H[MAXN] , *edge ;

int siz[MAXN] ;
int num[MAXN] ;
int root ;
int n ;

void clear () {
	edge = E ;
	clr ( H , 0 ) ;
}

void addedge ( int u , int v ) {
	edge -> v = v ;
	edge -> next = H[u] ;
	H[u] = edge ++ ;
}

void dfs ( int u , int fa = 0 ) {
	siz[u] = 1 ;
	num[u] = 0 ;
	travel ( e , H , u ) {
		int v = e -> v ;
		if ( v != fa ) {
			dfs ( v , u ) ;
			siz[u] += siz[v] ;
			if ( siz[v] > num[u] ) num[u] = siz[v] ;
		}
	}
	num[u] = max ( num[u] , n - siz[u] ) ;
	if ( num[u] < num[root] ) root = u ;
}

void solve () {
	int x , y ;
	scanf ( "%d" , &n ) ;
	num[root = 0] = n ;
	clear () ;
	rep ( i , 1 , n ) {
		scanf ( "%d%d" , &x , &y ) ;
		addedge ( x , y ) ;
		addedge ( y , x ) ;
	}
	dfs ( 1 ) ;
	printf ( "%d %d\n" , root , num[root] ) ;
}

int main () {
	int T ;
	scanf ( "%d" , &T ) ;
	while ( T -- ) solve () ;
	return 0 ;
}