bzoj1468 Tree

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<deque>
#include<set>
#include<map>
#include<ctime>
#define LL long long
#define inf 0x7fffffff
#define N 40010
using namespace std;
inline LL read()
{
    LL 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;
}
struct edge{int to,next,v;}e[10*N];
int head[N],son[N],f[N],d[N],s[N];
int n,k,cnt,root,sum,ans,len;
bool vis[N];
inline void ins(int u,int v,int w)
{
    e[++cnt].to=v;
    e[cnt].v=w;
    e[cnt].next=head[u];
    head[u]=cnt;
} 
inline void insert(int u,int v,int w)
{
    ins(u,v,w);
    ins(v,u,w);
}
inline void getroot(int x,int fa)
{
    son[x]=1;f[x]=0;
    for(int i=head[x];i;i=e[i].next)
        if (fa!=e[i].to&&!vis[e[i].to])
        {
            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 getd(int x,int fa)
{
    s[++len]=d[x];
    for (int i=head[x];i;i=e[i].next)
        if (!vis[e[i].to]&&fa!=e[i].to)
        {
            d[e[i].to]=d[x]+e[i].v;
            getd(e[i].to,x);
        }
}
inline int calc(int x,int v)
{
    d[x]=v;len=0;
    getd(x,0);
    sort(s+1,s+len+1);
    int tt=0,l=1,r=len;
    while (l<r)
    {
        if (s[l]+s[r]<=k)tt+=r-l,l++;
        else r--;
    }
    return tt;
}
inline void solve(int x)
{
    ans+=calc(x,0);vis[x]=1;
    for(int i=head[x];i;i=e[i].next)
        if (!vis[e[i].to])
        {
            ans-=calc(e[i].to,e[i].v);
            sum=son[e[i].to];
            root=0;
            getroot(e[i].to,0);
            solve(e[i].to);
        }
}
int main()
{
    n=read();
    for (int i=1;i<n;i++)
    {
        int x=read(),y=read(),z=read();
        insert(x,y,z);
    }
    k=read();
    f[0]=n+1;sum=n;
    getroot(1,0);
    solve(root);
    printf("%d\n",ans);
    return 0;
}