HDU 2680 Choose the best route(Dijkstra算法)


Choose the best route

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 12523    Accepted Submission(s): 4072


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
 
大體題意:
KiKi要去拜訪他的朋友,問最短路是多少。
其中s 是他朋友的編號。
與他自己相連的車站有很多。
思路:
直接設KiKi的編號為0,把相連的車站連起來,權值設為0,一遍Dijkstra算法即可!
注意 他的目標是S而不是n  (= =!)
到達不了輸出-1.

注意  該題目是有向圖!
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 1000 + 10;
const int INF = 1000000 + 10;
int g[maxn][maxn],d[maxn];
int n,m,s;
bool v[maxn];
void dijkstra(int s){
    memset(v,0,sizeof v);
    for (int i = 0; i <= n; ++i)d[i] = (i == s ? 0 : INF);
    for (int i = 0; i <= n; ++i){
        int x,m = INF;
        for (int y = 0; y <= n; ++y) if (!v[y] && d[y] <= m)m = d[x=y];
        v[x] = 1;
        for (int y = 0; y <= n; ++y) d[y]= min(d[y],d[x]+g[x][y]);
    }
}
int main(){
    while(scanf("%d%d%d",&n,&m,&s) == 3){
        for (int i = 0; i <= n; ++i)
            for (int j = 0; j <= n; ++j)
                g[i][j] = INF;
        for (int i = 0; i < m; ++i){
            int u,v,w;
            scanf("%d%d%d",&u,&v,&w);
            g[u][v] = min(g[u][v],w);
        }
        int k;
        scanf("%d",&k);
        for (int i = 0; i < k; ++i){
            int w;
            scanf("%d",&w);
            g[0][w] = 0;
        }
        dijkstra(0);
        printf("%d\n",d[s] == INF ? -1 : d[s]);
    }

    return 0;
}



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