点击打开链接

bfs,需要自己构图

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<vector>

using namespace std;

const int maxn = 100005;
int dep[ maxn ];
int vis[ maxn ];
int pre[ maxn ];
vector< int >mapp[ maxn ];

void Bfs( int s ){
	memset( dep, -1, sizeof( dep ) );
	dep[ 0 ] = 0;
	queue< int > q;
	q.push( s );
	while( !q.empty() ){
		int u = q.front();
		q.pop();
		int sz = mapp[ u ].size();
		for( int i = 0; i < sz; ++i ){
			int v = mapp[ u ][ i ];
			if( dep[ v ] != -1 )
				continue;
			
			dep[ v ] = dep[ u ] + 1
			q.push( v );
		}
	}
}

int main(){
	int Case, n, d, u, v;
	scanf( "%d", &Case );
	while( Case-- ){
		scanf( "%d%d", &n, &d );
		for( int i = 0; i < n; ++i )
			mapp[ i ].clear();
		for( int i = 1; i < n; ++i ){
			scanf( "%d%d", &u, &v );
			mapp[ u ].push_back( v );
			mapp[ v ].push_back( u );
		}
		Bfs( 0 );
		int ans = 0;
		for( int i = 0; i < n; ++i ){
			if( dep[ i ] > d ){
				ans++;
			}
		}
		printf( "%d\n", ans );
	}
	return 0;
}