【BZOJ1468】Tree [点分治]

  1 #include<iostream>  
  2 #include<algorithm>  
  3 #include<cstdio>  
  4 #include<cstring>  
  5 #include<cstdlib>  
  6 #include<cmath>  
  7 using namespace std;  
  8       
  9 const int ONE=80001;
 10   
 11 int n,K;
 12 int x,y,z;
 13 int next[ONE],first[ONE],go[ONE],w[ONE],tot;
 14 int center_vis[ONE];
 15 int Max,dist[ONE],num;
 16 int d[ONE];
 17 int center,Ans;
 18   
 19 int get()
 20 { 
 21         int res,Q=1;    char c;
 22         while( (c=getchar())<48 || c>57)
 23         if(c==‘-‘)Q=-1;
 24         if(Q) res=c-48; 
 25         while((c=getchar())>=48 && c<=57) 
 26         res=res*10+c-48; 
 27         return res*Q; 
 28 }
 29   
 30 int Add(int u,int v,int z)
 31 {
 32         next[++tot]=first[u];   first[u]=tot;   go[tot]=v;  w[tot]=z;
 33         next[++tot]=first[v];   first[v]=tot;   go[tot]=u;  w[tot]=z;
 34 }
 35   
 36 namespace PointF
 37 {
 38         struct power
 39         {
 40             int maxx,size;
 41         }S[ONE];
 42           
 43         void Getsize(int u,int father)
 44         {
 45                 S[u].size=1;
 46                 S[u].maxx=0;
 47                 for(int e=first[u];e;e=next[e])
 48                 {
 49                     int v=go[e];
 50                     if(v==father || center_vis[v]) continue;
 51                     Getsize(v,u);
 52                     S[u].size+=S[v].size;
 53                     S[u].maxx=max(S[u].maxx,S[v].size);
 54                 }
 55         }
 56           
 57         void Getcenter(int u,int father,int total)
 58         {
 59                 S[u].maxx=max(S[u].maxx,total-S[u].size);
 60                 if(Max>S[u].maxx)
 61                 {
 62                     Max=S[u].maxx;
 63                     center=u;
 64                 }
 65                   
 66                 for(int e=first[u];e;e=next[e])
 67                 {
 68                     int v=go[e];
 69                     if(v==father || center_vis[v]) continue;
 70                     Getcenter(v,u,total);
 71                 }
 72         }
 73           
 74         void Getdist(int u,int father,int value)
 75         {
 76                 dist[++num]=value;
 77                 for(int e=first[u];e;e=next[e])
 78                 {
 79                     int v=go[e];
 80                     if(v==father || center_vis[v]) continue;
 81                     Getdist(v,u,value+w[e]);
 82                 }
 83         }
 84           
 85         int Calc(int u,int value)
 86         {
 87             int res=0;
 88             num=0;
 89               
 90             Getdist(u,0,value);
 91             sort(dist+1,dist+num+1);
 92               
 93             int l=1,r=num;
 94               
 95             while(l<r)
 96             {
 97                 while(dist[l]+dist[r]>K && l<r) r--;
 98                 res+=r-l;
 99                 l++;
100             }
101             return res;
102         }
103           
104         void Dfs(int u)
105         {
106                 Max=n;  
107                 Getsize(u,0);
108                   
109                 center=u;
110                 Getcenter(u,0,S[u].size);
111                 center_vis[center]=true;
112                  
113                 Ans+=Calc(center,0);
114                 for(int e=first[center];e;e=next[e])
115                 {
116                     int v=go[e];
117                     if(center_vis[v]) continue;
118                     Ans-=Calc(v,w[e]);
119                     Dfs(v);
120                 }
121         }
122 }
123   
124   
125   
126 int main()
127 {
128         n=get();
129         for(int i=1;i<n;i++)
130         {
131             x=get();    y=get();    z=get();
132             Add(x,y,z);
133         }
134           
135         K=get();
136         PointF::Dfs(1);
137           
138         printf("%d",Ans);
139 }