http://acm.hdu.edu.cn/showproblem.php?pid=1548
1 //hdu 1548
2 #include<stdio.h>
3 #include<string.h>
4 #define INF 999999
5 int map[202][202],vis[202],dist[202],pre[202];
6 int n,a,b;
7 void dijkstra(int s)
8 {
9 for(int i=1;i<=n;i++)
10 {
11 vis[i]=0;
12 dist[i]=map[s][i];
13 pre[i]=s;
14 }
15 vis[s]=1;
16 dist[s]=0;
17 for(int i=1;i<n;i++)
18 {
19 int p=0,min=100000000;
20 for(int j=1;j<=n;j++)
21 if(!vis[j]&&dist[j]<min)
22 {
23 min=dist[j];
24 p=j;
25 }
26 vis[p]=1;
27 if(p==0) return;
28 for(int j=1;j<=n;j++)
29 if(!vis[j]&&map[p][j]+dist[p]<dist[j])
30 {
31 dist[j]=map[p][j]+dist[p];
32 pre[j]=p;
33 }
34 }
35
36 }
37 int main()
38 {
39 //freopen("in.txt","r",stdin);
40 while(scanf("%d",&n)!=EOF&&n)
41 {
42 int k[500];
43 scanf("%d%d",&a,&b);
44 memset(map,INF,sizeof(map));
45 for(int i=1;i<=n;i++)
46 {
47 scanf("%d",&k[i]);
48 if(i+k[i]<=n)
49 map[i][i+k[i]]=1;
50 if(i-k[i]>0)
51 map[i][i-k[i]]=1;
52 }
53 dijkstra(a);
54 if(dist[b]>INF)
55 printf("-1
");
56 else
57 printf("%d
",dist[b]);
58 }
59 return 0;
60 }