HDU-1548 A strange lift

 1 # include<iostream>
 2 # include<cstdio>
 3 # include<queue>
 4 # include<cstring>
 5 # include<algorithm>
 6 using namespace std;
 7 struct node
 8 {
 9     int pos,time;
10 };
11 int n,a,b;
12 int f[205];
13 int mark[205];
14 void BFS()
15 {
16     queue<node>q;
17     memset(mark,0,sizeof(mark));
18     node now;
19     now.pos=a,now.time=0;
20     q.push(now);
21     mark[a]=1;
22     while(!q.empty())
23     {
24         now=q.front();
25         q.pop();
26         if(now.pos==b){
27             printf("%d\n",now.time);
28             return ;
29         }
30         node nxt;
31         nxt.pos=now.pos+f[now.pos];
32         nxt.time=now.time+1;
33         if(nxt.pos<=n&&!mark[nxt.pos]){
34             q.push(nxt);
35             mark[nxt.pos]=1;
36         }
37         nxt.pos=now.pos-f[now.pos];
38         nxt.time=now.time+1;
39         if(nxt.pos>=1&&!mark[nxt.pos]){
40             q.push(nxt);
41             mark[nxt.pos]=1;
42         }
43     }
44     printf("-1\n");
45 }
46 int main()
47 {
48     while(scanf("%d",&n)&&n)
49     {
50         scanf("%d%d",&a,&b);
51         for(int i=1;i<=n;++i)
52             scanf("%d",&f[i]);
53         BFS();
54     }
55 }

 1 # include<iostream>
 2 # include<cstdio>
 3 # include<queue>
 4 # include<cstring>
 5 # include<algorithm>
 6 using namespace std;
 7 const int INF=1<<29;
 8 int mp[205][205];
 9 int f[205],a,b,n,dis[205];
10 void init()
11 {
12     for(int i=1;i<=n;++i)
13         for(int j=1;j<=n;++j)
14             mp[i][j]=(i==j)?0:INF;
15     for(int i=1;i<=n;++i){
16         if(i+f[i]<=n)
17             mp[i][i+f[i]]=1;
18         if(i-f[i]>=1)
19             mp[i][i-f[i]]=1;
20     }
21 }
22 void spfa()
23 {
24     init();
25     fill(dis+1,dis+n+1,INF);
26     queue<int>q;
27     q.push(a);
28     dis[a]=0;
29     while(!q.empty()){
30         int u=q.front();
31         q.pop();
32         for(int i=1;i<=n;++i){
33             if(dis[i]>dis[u]+mp[u][i]){
34                 dis[i]=dis[u]+mp[u][i];
35                 q.push(i);
36             }
37         }
38     }
39     if(dis[b]==INF)
40         printf("-1\n");
41     else
42         printf("%d\n",dis[b]);
43 }
44 int main()
45 {
46     while(scanf("%d",&n)&&n)
47     {
48         scanf("%d%d",&a,&b);
49         for(int i=1;i<=n;++i)
50             scanf("%d",f+i);
51         spfa();
52     }
53     return 0;
54 }