POJ 1985 Cow Marathon (树的直径) 模板

//9186307 NKHelloWorld 1985 Accepted 1824K 141MS C++ 1490B 2011-08-18 10:56:49
//9186317 NKHelloWorld 1985 Accepted 1824K 110MS C++ 1565B 2011-08-18 10:57:21
//9186348 NKHelloWorld 1985 Accepted 1888K 141MS G++ 1644B 2011-08-18 10:59:14
#include <cstdio>
#include <cstring>
#define MAXN 81000
int n,m;
struct EDGE
{
int to,dis,next;
}edge[MAXN];
int pt_edge = 0,index[41000],endpt = 1,ans = 0;

int que[MAXN],dis[MAXN];
bool visited[MAXN];
int bfs(int start)
{
int j;
int tail = 0,head = 0;
memset(visited,false,sizeof(visited));
dis[tail] = 0;
que[tail++] = start;
visited[start] = true;
while(head < tail)
{
for(j=index[que[head]];j!=-1;j=edge[j].next)
{
if(visited[edge[j].to]==false)
{
dis[tail] = dis[head] + edge[j].dis;
que[tail] = edge[j].to;
visited[que[tail]] = true;
if(dis[tail] > ans)
{
ans = dis[tail];
endpt = que[tail];
}
tail++;
}
}
head++;
}
return ans;
}

int main()
{
int i,j,f1,f2,dis;
char dir[5];
memset(index,-1,sizeof(index));
scanf("%d%d",&n,&m);
for(i=1;i<=m;i++)
{
scanf("%d%d%d%s",&f1,&f2,&dis,dir);
edge[pt_edge].next = index[f1]; index[f1] = pt_edge;
edge[pt_edge].to = f2;  edge[pt_edge++].dis = dis;
edge[pt_edge].next = index[f2]; index[f2] = pt_edge;
edge[pt_edge].to = f1;  edge[pt_edge++].dis = dis;
}
bfs(1);
printf("%d\n",bfs(endpt));
return 0;
}