HDU 1548 A strange lift

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 #include <algorithm>
 6 #include <climits>
 7 #include <vector>
 8 #include <queue>
 9 #include <cstdlib>
10 #include <string>
11 #include <set>
12 #include <stack>
13 #define LL long long
14 #define pii pair<int,int>
15 #define INF 0x3f3f3f3f
16 using namespace std;
17 struct node{
18     int p,step;
19     node(int x = 0,int y = 0):p(x),step(y){}
20 };
21 int N,A,B,k[210];
22 bool vis[210];
23 queue<node>q;
24 int bfs(){
25     while(!q.empty()) q.pop();
26     memset(vis,false,sizeof(vis));
27     vis[A] = true;
28     node temp(A,0);
29     q.push(temp);
30     int to;
31     while(!q.empty()){
32         node now = q.front();
33         q.pop();
34         if(now.p == B) return now.step;
35         to = now.p + k[now.p];
36         if(to <= N && !vis[to]){
37             vis[to] = true;
38             q.push(node(to,now.step+1));
39         }
40         to = now.p - k[now.p];
41         if(to > 0 && !vis[to]){
42             vis[to] = true;
43             q.push(node(to,now.step+1));
44         }
45     }
46     return -1;
47 }
48 int main() {
49     while(scanf("%d",&N),N){
50         scanf("%d %d",&A,&B);
51         for(int i = 1; i <= N; i++)
52             scanf("%d",k+i);
53         printf("%d\n",bfs());
54     }
55     return 0;
56 }