hdoj 2680 最短路（dijkstra）

Choose the best route

Problem Description

One day , Kiki wants to visit one of her friends. As she is liable to carsickness , she wants to arrive at her friend’s home as soon as possible . Now give you a map of the city’s traffic route, and the stations which are near Kiki’s home so that she can take. You may suppose Kiki can change the bus at any station. Please find out the least time Kiki needs to spend. To make it easy, if the city have n bus stations ,the stations will been expressed as an integer 1,2,3…n.

 

Input

There are several test cases. 
Each case begins with three integers n, m and s,(n<1000,m<20000,1=<s<=n) n stands for the number of bus stations in this city and m stands for the number of directed ways between bus stations .(Maybe there are several ways between two bus stations .) s stands for the bus station that near Kiki’s friend’s home.
Then follow m lines ,each line contains three integers p , q , t (0<t<=1000). means from station p to station q there is a way and it will costs t minutes .
Then a line with an integer w(0<w<n), means the number of stations Kiki can take at the beginning. Then follows w integers stands for these stations.

 

Output

The output contains one line for each data set : the least time Kiki needs to spend ,if it’s impossible to find such a route ,just output “-1”.

 

Sample Input

   
   
   
   

    
    
    
    5 8 5
1 2 2
1 5 3
1 3 4
2 4 7
2 5 6
2 3 5
3 5 1
4 5 1
2
2 3
4 3 4
1 2 3
1 3 4
2 3 2
1
1
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    1
-1
   
   
   
   

 

Author

dandelion

 

Source

2009浙江大学计算机研考复试（机试部分）——全真模拟

  找了2小时的错，最后我发现

路是单向的！！！

牢记教训！！！

起点不确定，终点确定，所以我们可以把终点当成起点，反着进行寻路过程，反正一样的- -，这样只要进行一次dijkstra就行

#include<cstdio>
#include<cstring>
using namespace std;
#define INF 0x3f3f3f3f
const int MAX=1010;
int dist[MAX],n,map[MAX][MAX],vis[MAX];
void Dijkstra(int s)
{
    int i,j,min,pos;
    memset(vis,0,sizeof(vis));
    for(i=1;i<=n;i++)
        dist[i]=map[s][i];
    dist[s]=0;
    vis[s]=1;
    for(i=1;i<=n;i++)
    {
        min=INF;
        for(j=1;j<=n;j++)
        {
            if(!vis[j]&&dist[j]<min)
                min=dist[pos=j];
        }
        if(min==INF)
            break;
        vis[pos]=1;
        for(j=1;j<=n;j++)
        {
            if(!vis[j]&&dist[pos]+map[pos][j]<dist[j])
                dist[j]=dist[pos]+map[pos][j];
        }
    }
}
int main()
{
    int i,e,a,b,c,x,y,m;
    while(scanf("%d%d%d",&n,&m,&e)!=EOF)
    {
        memset(map,INF,sizeof(map));
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            if(c<map[b][a])
                map[b][a]=c;
        }
        Dijkstra(e);
        scanf("%d",&x);
        int ans=INF;
        while(x--)
        {
            scanf("%d",&y);
            if(dist[y]<ans)
                ans=dist[y];
        }
        if(ans!=INF)
            printf("%d\n",ans);
        else
            printf("-1\n");
    }
    return 0;
}