hdu 2680 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 51 2 21 5 31 3 42 4 72 5 62 3 53 5 14 5 122 34 3 41 2 31 3 42 3 211

 

Sample Output

1-1

题意概况：Kiki要坐公交车去他的朋友家里，现在给你n个站点，m条路线，以及他朋友家所在的站点，和KIKI家附近的站点，求最少话费的时间。

解题思路：Kiki家附近可能有多个站点，不知道从哪个站点出发最省时，如果一个一个试的话会超时，但是无论从哪个站点出发到达的朋友家的点都只有一个，所以可以让从朋友家出发往Kiki家的方向走，最后比较到Kiki家附近的站点哪个最省时。

代码：

#include<stdio.h>#include<string.h>#define N 1500#define INF 0x3f3f3fint n,t,f;int map[N][N]; int s[N];int book[N];int d[N];void Dijkstra(int x){int i,j;memset(book,0,sizeof(book));book[x]=1;for(i=1;i<=n;i++){d[i]=map[x][i];}d[x]=0;for(i=1;i<=n;i++){int index=-1;int max=INF;for(j=1;j<=n;j++){if(book[j]==0&&d[j]<max){max=d[j];index=j;}}if(index==-1)break;book[index]=1;for(j=1;j<=n;j++){if(book[j]==0&&d[j]>map[index][j]+max){d[j]=map[index][j]+max;}}}int max=INF;for(int k=1;k<=f;k++){if(max>d[s[k]])max=d[s[k]];}//printf("%d ",d[i]);//printf("\n");if(max>=INF)printf("-1\n");elseprintf("%d\n",max);}int main(){int i,j,k,m,u,v,w;while(scanf("%d%d%d",&n,&m,&t)!=EOF){memset(map,INF,sizeof(map));for(i=0;i<m;i++){scanf("%d%d%d",&u,&v,&w);if(w<map[v][u]){map[v][u]=w;}}scanf("%d",&f);for(i=1;i<=f;i++){scanf("%d",&s[i]);}Dijkstra(t);}return 0;}