bzoj 1468

点分模板，答案随便加加减减（为啥计划里留了一题最简单的没写）

#include<cstdio>
#include<algorithm>
#include<cstring>
#define N 16384
using namespace std;
inline void read(int &a){
	int f=a=0;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-') f=1;ch=getchar();}
	while(ch<='9'&&ch>='0') a=a*10+ch-'0',ch=getchar();
	if(f) a=-a;
}
int n,k,s,len;
int nex[N<<1],beg[N],to[N<<1],va[N<<1];
bool done[N];
int er[N],siz[N],root;
int cnt,jl[N];
int ans;
inline void Add(int a,int b,int c){
	nex[++len]=beg[a],beg[a]=len,to[len]=b,va[len]=c;
	nex[++len]=beg[b],beg[b]=len,to[len]=a,va[len]=c;
}
void dfs1(int p,int fa){
	siz[p]=1;er[p]=0;
	for(int i=beg[p];i;i=nex[i]){
		if(to[i]!=fa&&!done[to[i]]){
			dfs1(to[i],p);
			siz[p]+=siz[to[i]];
			er[p]=max(er[p],siz[to[i]]);
		}
	}
	er[p]=max(er[p],s-siz[p]);
	if(!root||er[p]<er[root]) root=p;
}
void dfs2(int p,int fa,int dis){
	jl[cnt++]=dis;
	for(int i=beg[p];i;i=nex[i])
		if(to[i]!=fa&&!done[to[i]])
			dfs2(to[i],p,dis+va[i]);
}
int calc(int p,int v){
	int ans=0;
	cnt=0;
	dfs2(p,0,v);
	sort(jl,jl+cnt);
	for(int l=0,r=cnt-1;l<r;l++){
		while(jl[l]+jl[r]>k&&l<r) r--;
		ans+=r-l;
	}
	return ans;
}
void df(int p){ 
	done[p]=1;
	ans+=calc(p,0);
	for(int i=beg[p];i;i=nex[i]){
		if(!done[to[i]]){
			ans-=calc(to[i],va[i]);
			s=siz[to[i]],root=0;
			dfs1(to[i],0);
			df(root);
		}
	}
}
int main(){
	er[0]=1008610086;
	while(scanf("%d%d",&n,&k)){
		if(!n) break;
		memset(beg,0,sizeof(beg));
		memset(done,0,sizeof(done));
		len=ans=root=0;
		for(int i=1,a,b,c;i<n;i++){
			read(a);read(b);read(c);
			Add(a,b,c);
		}
		dfs1(1,0);
		df(root);
		printf("%d\n",ans);
	}
	return 0;
}