hdu2196 Computer

来源：互联网发布：食品安全事故数据统计编辑：程序博客网时间：2024/05/21 00:47
求树的所有结点的最长直径
#include<iostream>#include<cstring>#include<cstdio>using namespace std;#define M 10010int len[M],len2[M],leaf[M],leaf2[M],head[M];int n,tot;struct node{    int to,dis,next;}edge[M*2];void insert(int u,int v,int dis){    edge[tot].to=v;    edge[tot].dis=dis;    edge[tot].next=head[u];    head[u]=tot++;}void dfs(int u,int pre){    int i,v;    for(i=head[u];i!=-1;i=edge[i].next){        v=edge[i].to;        if(v==pre) continue;        dfs(v,u);        if(len[v]+edge[i].dis>len[u]){            len2[u]=len[u];            leaf2[u]=leaf[u];            len[u]=len[v]+edge[i].dis;            leaf[u]=v;        }        else if(len[v]+edge[i].dis>len2[u]){            len2[u]=len[v]+edge[i].dis;            leaf2[u]=v;        }    }}void dfs2(int u,int pre){    int i,v;    for(i=head[u];i!=-1;i=edge[i].next){        v=edge[i].to;        if(v==pre) continue;        if(leaf[u]==v){            if(len2[u]+edge[i].dis>len[v]){                len2[v]=len[v];                leaf2[v]=leaf[v];                len[v]=len2[u]+edge[i].dis;                leaf[v]=u;            }            else if(len2[u]+edge[i].dis>len2[v]){                len2[v]=len2[u]+edge[i].dis;                leaf2[v]=u;            }        }        else{            if(len[u]+edge[i].dis>len[v]){                len2[v]=len[v];                leaf2[v]=leaf[v];                len[v]=len[u]+edge[i].dis;                leaf[v]=u;            }            else if(len[u]+edge[i].dis>len2[v]){                len2[v]=len[u]+edge[i].dis;                leaf2[v]=u;            }        }        dfs2(v,u);    }}int main(){    int v,dis;    while(scanf("%d",&n)!=EOF){        tot=0;        memset(head,-1,sizeof(head));        memset(len,0,sizeof(len));        memset(len2,0,sizeof(len2));        memset(leaf,-1,sizeof(leaf));        for(int i=2;i<=n;i++){            scanf("%d%d",&v,&dis);            insert(i,v,dis);            insert(v,i,dis);        }        dfs(1,-1);        dfs2(1,-1);        for(int i=1;i<=n;i++)            printf("%d\n",len[i]);    }    return 0;}