poj2631 树的直径 + bfs

 //Accepted    492 KB    0 ms
 //树的直径 bfs
 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <queue>
 using namespace std;
 ;
 struct node
 {
     int u,v,c;
     node()
     {

     }
     node(int u,int v,int c):u(u),v(v),c(c)
     {

     }
 }p[*imax_n];
 int e;
 int head[imax_n];
 ];
 void addEdge(int u,int v,int c)
 {
     p[e]=node(u,v,c);
     next[e]=head[u];
     head[u]=e++;
 }
 void init()
 {
     memset(head,-,sizeof(head));
     memset(next,-,sizeof(next));
     e=;
 }
 bool vis[imax_n];
 int dis[imax_n];
 queue<int >q;
 int bfs(int s)
 {
     ;
     int temp_node;
     while (!q.empty()) q.pop();
     memset(vis,,sizeof(vis));
     q.push(s);
     vis[s]=;
     memset(dis,,sizeof(dis));
     while (!q.empty())
     {
         int x=q.front();
         q.pop();
         if (dis[x]>ans)
         {
             ans=dis[x];
             temp_node=x;
         }
         ;i=next[i])
         {
             int y=p[i].v;
             if (!vis[y])
             {
                 vis[y]=;
                 q.push(y);
                 if (dis[x]+p[i].c>dis[y])
                 dis[y]=dis[x]+p[i].c;
             }
         }
     }
     return temp_node;
 }
 int main()
 {
     int x,y,c;
     init();
     while (scanf("%d%d%d",&x,&y,&c)!=EOF)
     //for (int i=0;i<5;i++)
     {
         //scanf("%d%d%d",&x,&y,&c);
         addEdge(x,y,c);
         addEdge(y,x,c);
     }
     x=bfs();
     y=bfs(x);
     printf("%d\n",dis[y]);
     ;
 }