uva10000 Longest Paths

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define N 1000
using namespace std;
int g

;
int dis
;
int vis
;
void spfa(int n,int s){
queue<int>que;
while(!que.empty()){
que.pop();
}
que.push(s);
while(!que.empty()){
int d=que.front();
que.pop();
vis[d]=0;
for(int i=1;i<=n;i++){
if(g[d][i]>0 && dis[i]<dis[d]+g[d][i]){
dis[i]=dis[d]+g[d][i];
if(!vis[i]){
vis[i]=1;
que.push(i);
}
}
}
}
int l=1;
for(int i=1;i<=n;i++){
if(dis[i]>dis[l]){
l=i;
}
}
printf("The longest path from %d has length %d, finishing at %d.\n\n",s,dis[l],l);
}
int main()
{
int n;
int counter=0;
while(~scanf("%d",&n) && n!=0){
counter++;
int s;
scanf("%d",&s);
int u,v;
memset(g,0,sizeof(g));
memset(dis,0,sizeof(dis));
memset(vis,0,sizeof(vis));
while(scanf("%d%d",&u,&v) && (u!= 0 && v!=0)){
g[u][v]=1;
}
printf("Case %d: ",counter);
spfa(n,s);
}
return 0;
}