POJ1741 Tree （点分治）

Tree

Time Limit: 1000MS		Memory Limit: 30000K
Total Submissions: 25772		Accepted: 8566

Description

Give a tree with n vertices,each edge has a length(positive integer less than 1001). 
Define dist(u,v)=The min distance between node u and v. 
Give an integer k,for every pair (u,v) of vertices is called valid if and only if dist(u,v) not exceed k. 
Write a program that will count how many pairs which are valid for a given tree. 

Input

The input contains several test cases. The first line of each test case contains two integers n, k. (n<=10000) The following n-1 lines each contains three integers u,v,l, which means there is an edge between node u and v of length l. 
The last test case is followed by two zeros. 

Output

For each test case output the answer on a single line.

Sample Input

5 4
1 2 3
1 3 1
1 4 2
3 5 1
0 0

Sample Output

8

code

 #include<cstdio>
 #include<algorithm>
 #include<cstring>

 using namespace std;

 const int N = ;

 struct Edge{
     int to,nxt,w;
 }e[N<<];
 int head[N],son[N],f[N],deth[N],d[N];
 bool vis[N];
 int ans,tot,Root,sum,n,k;

 void init() {
     memset(head,,sizeof(head));
     memset(vis,false,sizeof(vis));
     ans = tot = Root = ;
 }
 void add_edge(int u,int v,int w) {
     e[++tot].to = v;e[tot].w = w;e[tot].nxt = head[u];head[u] = tot;
 }
 void getroot(int u,int pa) {
     son[u] = ;f[u] = ;
     for (int i=head[u]; i; i=e[i].nxt) {
         int v = e[i].to;
         if (v==pa||vis[v]) continue;
         getroot(v,u);
         son[u] += son[v];
         f[u] = max(f[u],son[v]);
     }
     f[u] = max(f[u],sum-son[u]);
     if (f[u] < f[Root]) Root = u;
 }
 void getdeth(int u,int pa) {
     deth[++deth[]] = d[u];
     for (int i=head[u]; i; i=e[i].nxt) {
         int v = e[i].to,w = e[i].w;
         if (v==pa||vis[v]) continue;
         d[v] = d[u] + w;
         getdeth(v,u);
     }
 }
 int calcc(int u,int w) {
     deth[] = ;
     d[u] = w;
     getdeth(u,);
     sort(deth+,deth+deth[]+);
     int l = ,r = deth[],ret = ;
     while (l < r) {
         if (deth[l] + deth[r] <= k) ret += r-l,l++;
         else r--;
     }
     return ret;
 }
 void work(int u) {
     ans += calcc(u,);
     vis[u] = ;
     for (int i=head[u]; i; i=e[i].nxt) {
         int v = e[i].to,w = e[i].w;
         if (vis[v]) continue;
         ans -= calcc(v,w);
         sum = son[v];
         Root = ;
         getroot(v,);
         work(Root);
     }
 }
 int main() {
     while (scanf("%d%d",&n,&k)!=EOF && !(n==&&k==)) {
         init();
         for (int a,b,c,i=; i<n; ++i) {
             scanf("%d%d%d",&a,&b,&c);
             add_edge(a,b,c);add_edge(b,a,c);
         }
         f[] = 1e9;
         sum = n;
         getroot(,);
         work(Root);
         printf("%d\n",ans);
     }
     return ;
 }