POJ 2631 Roads in the North

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int maxn=10000+100;int len,ans,cnt=0,p[maxn],son[maxn],head[maxn],vis[maxn],weigh[maxn][maxn];struct node{    int u,v,next;}node[2*maxn];void add(int u,int v){    node[cnt].u=u;node[cnt].v=v;    node[cnt].next=head[u];    head[u]=cnt++;    node[cnt].u=v;node[cnt].v=u;    node[cnt].next=head[v];    head[v]=cnt++;}void dfs(int u){    vis[u]=1;    for(int i=head[u];i!=-1;i=node[i].next)    {        if(u==1) son[u]=0;        int v=node[i].v;        if(vis[v]) continue;        dfs(v);        son[u]=max(son[u],son[v]+weigh[u][v]);        if(u==1) p[len++]=son[1];    }}int main(){    int u,v,w;    memset(head,-1,sizeof(head));    memset(vis,0,sizeof(vis));    memset(son,0,sizeof(son));    while(scanf("%d%d%d",&u,&v,&w)!=EOF)    {        weigh[u][v]=w;        weigh[v][u]=w;        add(u,v);    }    ans=(1<<30);    dfs(1);    sort(p,p+len);    printf("%d",p[len-1]+p[len-2]);    printf("\n");    return 0;}