[Poj1741]Tree (点分治)

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#define inf 0x7fffffff
using namespace std;
inline int read(){
int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
return x*f;
}
int n,K,cnt,sum,ans,root;
int head[10001],deep[10001],d[10001],f[10001],son[10001];
bool vis[10001];
struct edge{int to,next,v;}e[20001];
inline void ins(int u,int v,int w){
e[++cnt]=(edge){v,head[u],w};head[u]=cnt;
e[++cnt]=(edge){u,head[v],w};head[v]=cnt;
}
inline void getroot(int x,int fa){
son[x]=1;f[x]=0;
for(int i=head[x];i;i=e[i].next){
if(e[i].to==fa||vis[e[i].to])continue;
getroot(e[i].to,x);
son[x]+=son[e[i].to];
f[x]=max(f[x],son[e[i].to]);
}
f[x]=max(f[x],sum-son[x]);
if(f[x]<f[root])root=x;
}
inline void getdeep(int x,int fa){
deep[++deep[0]]=d[x];
for(int i=head[x];i;i=e[i].next){
if(e[i].to==fa||vis[e[i].to])continue;
d[e[i].to]=d[x]+e[i].v;
getdeep(e[i].to,x);
}
}
inline int cal(int x,int now){
d[x]=now;deep[0]=0;
getdeep(x,0);
sort(deep+1,deep+deep[0]+1);
int t=0,l,r;
for(l=1,r=deep[0];l<r;){
if(deep[l]+deep[r]<=K)t+=r-l,l++;
else r--;
}
return t;
}
inline void work(int x){
ans+=cal(x,0);
vis[x]=1;
for(int i=head[x];i;i=e[i].next){
if(vis[e[i].to])continue;
ans-=cal(e[i].to,e[i].v);
sum=son[e[i].to];
root=0;
getroot(e[i].to,root);
work(root);
}
}
int main(){
while(1){
ans=root=cnt=0;
memset(vis,0,sizeof(vis));
memset(head,0,sizeof(head));
n=read();K=read();
if(n==0)break;
for(int i=1;i<n;++i){
int u=read(),v=read(),w=read();
ins(u,v,w);
}
sum=n;f[0]=inf;
getroot(1,0);
work(root);
printf("%d\n",ans);
}
return 0;
}