POJ 3268 Silver Cow Party

Find the longest route to and from.

Two SPFA times, and then select the maximum number of rounds and forth between a certain point. (Directed Graph)

Dijkstra + the adjacent matrix makes it easier to establish an undirected graph.

I use SPFA + two adjacent tables (positive and reverse), C ++ 32 ms.

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            #define INF 0x7fffffff#define eps 1e-6using namespace std;int n,m,start;struct lx{ int v,t;};vector
            
             g1[1001];vector
             
              g2[1001];int dis1[1001];int dis2[1001];void SPFA(int *dis,vector
              
               g[]){ bool vis[1001]; queue
               
                q; for(int i=1;i<=n;i++) dis[i]=INF,vis[i]=0; vis[start]=1,dis[start]=0; q.push(start); while(!q.empty()) { int u=q.front();q.pop(); vis[u]=0; for(int j=0;j
                
                 dis[u]+t) { dis[v]=dis[u]+t; if(!vis[v]) { vis[v]=1; q.push(v); } } } }}int main(){ while(scanf("%d%d%d",&n,&m,&start)!=EOF) { for(int i=1;i<=n;i++) g1[i].clear(),g2[i].clear(); while(m--) { int u,v,t; scanf("%d%d%d",&u,&v,&t); lx now; now.v=v,now.t=t; g1[u].push_back(now); now.v=u; g2[v].push_back(now); } SPFA(dis1,g1); SPFA(dis2,g2); int ans=0; for(int i=1;i<=n;i++) ans=max(ans,dis1[i]+dis2[i]); printf("%d\n",ans); }}