洛谷P4185 [USACO18JAN]MooTube G

题链

利用并查集，只有当该边的权值大于等于k值时才合并；

将输入扒下来按相关度从大到小排序，一个个更新即可

//#pragma GCC optimize("O2")
#include <bits/stdc++.h>
using namespace std;
//#include<ext/rope>
//using namespace __gnu_cxx;
//#include <ext/pb_ds/priority_queue.hpp>
//using namespace __gnu_pbds;
#define Combine Pair, greater<Pair>, pairing_heap_tag
#define LL long long
#define ll long long
#define Pair pair<double,LL>
#define ULL unsigned long long
#define ls rt<<1
#define rs rt<<1|1
#define one first
#define two second
#define MS 1000009
#define INF 1e9
#define DBINF 1e100
#define Pi acos(-1.0)
#define eps 1e-9
#define mod 1000000007
#define mod1 39989
#define mod2 1000000000

int n,m;
int fa[MS];
int size[MS];
int ac[MS];
struct node{
	int u,v,val;
}p[MS];
struct nod{
	int k,poi,pos;
}a[MS];

int find(int x){
	if(x == fa[x]) return x;
	else return fa[x] = find(fa[x]);
}

void merge(int x,int y){
	int fx = find(x);
	int fy = find(y);
	fa[fy] = fx;
	size[fx] += size[fy];
} 

int main() {
	ios::sync_with_stdio(false);
	cin >> n >> m;
	for(int i=1;i<=n-1;i++){
		cin >> p[i].u >> p[i].v >> p[i].val;
		if(p[i].u > p[i].v) swap(p[i].u,p[i].v);
		fa[i] = i;
		size[i] = 1;
	}
	size[n] = 1;
	fa[n] = n;
	
	sort(p+1,p+n+1,[](node t1,node t2){return t1.val > t2.val;});
	for(int i=1;i<=m;i++){
		cin >> a[i].k >> a[i].poi;
		a[i].pos = i;
	}
	sort(a+1,a+m+1,[](nod t1,nod t2){return t1.k > t2.k;});
	int i=1,j=1;
	for(;i<=m;i++){
		for(;j<=n && p[j].val>=a[i].k;j++){
			merge(p[j].u,p[j].v);
		}
		ac[a[i].pos] = size[find(a[i].poi)] - 1;
	}
	for(int i=1;i<=m;i++){
		cout << ac[i] << endl;
	}
	cout << endl;
	
	
	return 0; 
}