POJ1741 Tree + BZOJ1468 Tree 【点分治】

POJ1741 Tree + BZOJ1468 Tree


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


BZOJ上的和POJ上的其实差不多,只是输入输出格式的区别

然后就是点分治的板子
但是dcy说这题卡常,我也不知道为什么

我也没有卡啊


POJ1741:

#include<iostream>
#include<vector>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
#define N 40010
int n,k,cnt,rt,siz_tree,ans;
int siz[N],F[N],dis[N],head[N],val[N];
bool vis[N];
struct Edge{int v,w,next;}E[N<<1];
void init(){
    cnt=0;ans=0;
    memset(head,0,sizeof(head));
    memset(dis,0,sizeof(dis));
    memset(vis,0,sizeof(vis));//******
}
void add(int u,int v,int w){
    cnt++;
    E[cnt].v=v;
    E[cnt].w=w;
    E[cnt].next=head[u];
    head[u]=cnt;
}
void getroot(int u,int fa){
    siz[u]=1;F[u]=0;
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(vis[v]||v==fa)continue;
        getroot(v,u);
        siz[u]+=siz[v];
        F[u]=max(F[u],siz[v]);
    }
    F[u]=max(F[u],siz_tree-siz[u]);
    if(F[u]<F[rt])rt=u;
}
void getdis(int u,int fa){
    val[++val[0]]=dis[u];
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(v==fa||vis[v])continue;
        dis[v]=dis[u]+E[i].w;
        getdis(v,u);
    }
}
int work(int u,int pre){
    val[0]=0;dis[u]=pre;
    getdis(u,0);
    sort(val+1,val+val[0]+1);
    int l=1,r=val[0],res=0;
    while(l<r){
        if(val[r]+val[l]<=k)res+=r-l,l++;
        else r--;
    }
    return res;
}
void solve(int u){
    ans+=work(u,0);
    vis[u]=1;
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(vis[v])continue;
        ans-=work(v,E[i].w);
        F[rt=0]=siz_tree=siz[v];
        getroot(v,0);
        solve(rt);
    }
}
int main(){
    while(1){
        scanf("%d%d",&n,&k);
        if(!n&&!k)return 0;
        init();
        for(int i=1;i<n;i++){
            int u,v,w;
            scanf("%d%d%d",&u,&v,&w);
            add(u,v,w);
            add(v,u,w);
        }
        F[rt=0]=siz_tree=n;
        getroot(1,0);
        solve(rt);
        printf("%d\n",ans);
    }
    return 0;
}

BZOJ1468:

#include<iostream>
#include<vector>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
#define N 40010
int n,k,cnt,rt,siz_tree,ans;
int siz[N],F[N],dis[N],head[N],val[N];
bool vis[N];
struct Edge{int v,w,next;}E[N<<1];
void init(){
    cnt=0;ans=0;
    memset(head,0,sizeof(head));
    memset(dis,0,sizeof(dis));
    memset(vis,0,sizeof(vis));//******
}
void add(int u,int v,int w){
    cnt++;
    E[cnt].v=v;
    E[cnt].w=w;
    E[cnt].next=head[u];
    head[u]=cnt;
}
void getroot(int u,int fa){
    siz[u]=1;F[u]=0;
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(vis[v]||v==fa)continue;
        getroot(v,u);
        siz[u]+=siz[v];
        F[u]=max(F[u],siz[v]);
    }
    F[u]=max(F[u],siz_tree-siz[u]);
    if(F[u]<F[rt])rt=u;
}
void getdis(int u,int fa){
    val[++val[0]]=dis[u];
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(v==fa||vis[v])continue;
        dis[v]=dis[u]+E[i].w;
        getdis(v,u);
    }
}
int work(int u,int pre){
    val[0]=0;dis[u]=pre;
    getdis(u,0);
    sort(val+1,val+val[0]+1);
    int l=1,r=val[0],res=0;
    while(l<r){
        if(val[r]+val[l]<=k)res+=r-l,l++;
        else r--;
    }
    return res;
}
void solve(int u){
    ans+=work(u,0);
    vis[u]=1;
    for(int i=head[u];i;i=E[i].next){
        int v=E[i].v;
        if(vis[v])continue;
        ans-=work(v,E[i].w);
        F[rt=0]=siz_tree=siz[v];
        getroot(v,0);
        solve(rt);
    }
}
int main(){
    scanf("%d",&n);
    init();
    for(int i=1;i<n;i++){
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        add(u,v,w);
        add(v,u,w);
    }
    scanf("%d",&k);
    F[rt=0]=siz_tree=n;
    getroot(1,0);
    solve(rt);
    printf("%d\n",ans);
    return 0;
}
posted @ 2018-07-29 21:12  Dream_maker_yk  阅读(105)  评论(0编辑  收藏  举报