poj1135最短路

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <climits>
#include <string>
#include <iostream>
#include <map>
#include <cstdlib>
#include <list>
#include <set>
#include <queue>
#include <stack>

using namespace std;

int n,m;
const int maxn=505;
struct Node
{
    int x;int val;
}node[maxn];
struct cmp
{
    bool operator ()(const Node &a,const Node &b)
    {
        return a.val<b.val;
    }
};
const int INF=10000000;
int dis[maxn];
int vis[maxn];
int Map[maxn][maxn];
void djs(int x)
{
    for(int i=1;i<=n;i++){
        dis[i]=INF;vis[i]=0;
    }
    dis[x]=0;vis[x]=1;
    Node k; k.x=x;k.val=0;
    priority_queue<Node,vector<Node> ,cmp> q;
    q.push(k);
    while(!q.empty()){
        Node k=q.top();q.pop(); int cur=k.x;vis[x]=1;
        for(int i=1;i<=n;i++){
            if(dis[i]>dis[cur]+Map[cur][i]){
                dis[i]=dis[cur]+Map[cur][i];
                if(!vis[i]){
                    Node k; k.x=i;k.val=dis[i];
                    q.push(k);
                }
            }
        }
    }
}
int main()
{
    int ret=0;
    while(cin>>n>>m,++ret&&n||m){
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
            Map[i][j]=INF;
        for(int i=0;i<m;i++){
            int a,b,c;cin>>a>>b>>c;
            if(Map[a][b]>c) Map[a][b]=Map[b][a]=c;
        }
        djs(1);
        double ans=0;int sign=1;
        for(int i=1;i<=n;i++)
        if(dis[i]>ans){
            ans=dis[i];sign=i;
        }
        double ans1=0;int a;int b;
        for(int i=1;i<=n;i++){
            for(int j=i+1;j<=n;j++)if(Map[i][j]!=INF) {
                double t=(dis[i]+dis[j]+Map[i][j])/2.0;
                if(t>ans1) {
                    ans1=t; a=i;b=j;
                }
            }
        }
      //  for(int i=1;i<=n;i++)
          //  cout<<dis[i]<<endl;
        if(ret!=1) cout<<endl;
        printf("System #%d\n",ret);
        if(ans1>ans){
            printf("The last domino falls after %.1f seconds, between key dominoes %d and %d.\n",ans1,a,b);
        }
        else{
            printf("The last domino falls after %.1f seconds, at key domino %d.\n",ans,sign);
        }
    }
    return 0;
}