bzoj 1468 Tree 点分

Tree

Time Limit: 10 Sec  Memory Limit: 64 MB
Submit: 1972  Solved: 1101
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Description

给你一棵TREE,以及这棵树上边的距离.问有多少对点它们两者间的距离小于等于K

Input

N（n<=40000） 接下来n-1行边描述管道，按照题目中写的输入 接下来是k

Output

一行，有多少对点之间的距离小于等于k

Sample Input

7
1 6 13
6 3 9
3 5 7
4 1 3
2 4 20
4 7 2
10

Sample Output

5

HINT

 题解：点分模板题

 #include<cstring>
 #include<algorithm>
 #include<iostream>
 #include<cstdio>
 #include<cmath>

 #define N 40007
 #define inf 1000000007
 using namespace std;
 inline int read()
 {
     int x=,f=;char ch=getchar();
     while(!isdigit(ch)){if(ch=='-')f=-;ch=getchar();}
     while(isdigit(ch)){x=(x<<)+(x<<)+ch-'';ch=getchar();}
     return x*f;
 }

 int n,k,ans,id,total;
 int cnt,hed[N],rea[N<<],nxt[N<<],val[N<<];
 int tot,num[N],siz[N],f[N];
 bool vis[N];

 void add(int u,int v,int z)
 {
     nxt[++cnt]=hed[u];
     hed[u]=cnt;
     rea[cnt]=v;
     val[cnt]=z;
 }
 void get_heart(int u,int fa)
 {
     siz[u]=,f[u]=;
     for (int i=hed[u];i!=-;i=nxt[i])
     {
         int v=rea[i];
         if (v==fa||vis[v]) continue;
         get_heart(v,u);
         siz[u]+=siz[v];
         f[u]=max(f[u],siz[v]);
     }
     f[u]=max(f[u],total-f[u]);
     if (f[u]<f[id]) id=u;
 }
 void dfs_dep(int u,int now,int fa)
 {
     num[++tot]=now;
     for (int i=hed[u];i!=-;i=nxt[i])
     {
         int v=rea[i],fee=val[i];
         if (v==fa||vis[v]) continue;
         dfs_dep(v,now+fee,u);
     }
 }
 int calc(int u,int now)
 {
     tot=;int res=;
     dfs_dep(u,now,);
     sort(num+,num+tot+);
     int l=,r=tot;
     while(l<r)
     {
         if (num[l]+num[r]<=k) res+=r-l,l++;
         else r--;
     }
     return res;
 }
 void solve(int u)
 {
     ans+=calc(u,);
     vis[u]=true;
     for (int i=hed[u];i!=-;i=nxt[i])
     {
         int v=rea[i],fee=val[i];
         if (vis[v]) continue;
         ans-=calc(v,fee);
         total=siz[v],id=;
         get_heart(v,u);
         solve(v);
     }
 }
 int main()
 {
     memset(hed,-,sizeof(hed));
     n=read();
     for (int i=;i<n;i++)
     {
         int x=read(),y=read(),z=read();
         add(x,y,z);
         add(y,x,z);
     }
     k=read();
     total=n,f[]=inf;
     get_heart(,-);
     solve(id);
     printf("%d\n",ans);
 }