POJ 1741 Tree (树上点分治)（楼教主男人八题之一）

来源：互联网发布：手机桌面清理软件编辑：程序博客网时间：2024/05/21 22:21

题目地址：POJ 1741
树分治第一发！
树分治详情请看漆子超的国家集训队论文，论文传送门
树分治裸题。
代码如下：

#include <iostream>#include <string.h>#include <math.h>#include <queue>#include <algorithm>#include <stdlib.h>#include <map>#include <set>#include <stdio.h>#include <time.h>using namespace std;#define LL __int64#define pi acos(-1.0)//#pragma comment(linker, "/STACK:1024000000")const int mod=1e9+7;const int INF=0x3f3f3f3f;const double eqs=1e-9;const int MAXN=10000+10;int head[MAXN], cnt, ans, min1, root, tot;int siz[MAXN], dep[MAXN], vis[MAXN], d[MAXN];int n, k;struct node{        int v, w, next;}edge[MAXN<<1];void add(int u, int v, int w){        edge[cnt].v=v;        edge[cnt].w=w;        edge[cnt].next=head[u];        head[u]=cnt++;}void init(){        memset(head,-1,sizeof(head));        cnt=ans=0;        memset(vis,0,sizeof(vis));}void getroot(int u, int fa, int s){        int i, max1=0;        siz[u]=1;        for(i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                getroot(v,u,s);                siz[u]+=siz[v];                max1=max(max1,siz[v]);        }        max1=max(max1,s-siz[u]);        if(min1>max1){                min1=max1;                root=u;        }}void getdep(int u, int fa){        d[tot++]=dep[u];siz[u]=1;        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa||vis[v]) continue ;                dep[v]=dep[u]+edge[i].w;                getdep(v,u);                siz[u]+=siz[v];        }}int Cal(int u, int len){        int l, r, res=0;        tot=0;        dep[u]=len;        getdep(u,-1);        sort(d,d+tot);        r=tot-1;        for(l=0;l<tot;l++){                while(d[r]+d[l]>k) r--;                if(r<=l) break;                res+=r-l;        }        return res;}void work(int u){        ans+=Cal(u,0);        vis[u]=1;        for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(vis[v]) continue ;                ans-=Cal(v,edge[i].w);                min1=INF;                getroot(v,-1,siz[v]);                work(root);        }}int main(){        int u, v, w, i;        while(scanf("%d%d",&n,&k)!=EOF&&n+k){                init();                for(i=1;i<n;i++){                        scanf("%d%d%d",&u,&v,&w);                        add(u,v,w);                        add(v,u,w);                }                min1=INF;                getroot(1,-1,n);                work(root);                printf("%d\n",ans);        }        return 0;}

1 0