uva10000 Longest Paths

最长路径，和最短路径差不多，用了spfa来求

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define N 1000
using namespace std;
int g[N][N];
int dis[N];
int vis[N];
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;
}