hdu 1548 A strange lift

http://acm.hdu.edu.cn/showproblem.php?pid=1548

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>

using namespace std;

struct Node
{
int f;
int i;
};

int floor[210];
int yn[210];

int Bfs(int n, int a, int b)
{
Node now,next;
queue<Node> q;
now.f = a;
now.i = 0;
q.push(now);
while(!q.empty())
{
now = q.front();
q.pop();
yn[now.f] = 2;   //标记此楼已经到达
//       printf("%d %d\n",now.f,now.i);
if(now.f == b)   //判断是否到达指定楼层
{
return now.i;
}
else
{
next.i = now.i+1;
next.f = now.f+floor[now.f];   //向上走
if(next.f > 0 && next.f <= 200 && yn[next.f] == 0)
{
yn[next.f] = 1;   //标记此楼
q.push(next);
}
next.f = now.f-floor[now.f];   //向下走
if(next.f > 0 && next.f <= 200 && yn[next.f] == 0)
{
yn[next.f] = 1;   //标记此楼
q.push(next);
}
}
}
return -1;
}

int main()
{
int n,a,b;
int i,num;
while(scanf("%d",&n)&&n)
{
memset(yn,0,sizeof(yn));
for(i = 0; i< 210; i++)
{
floor[i] = 1000;
}
scanf("%d%d",&a,&b);
for(i = 1; i <= n; i++)
{
scanf("%d",&floor[i]);
}
num = Bfs(n,a,b);
printf("%d\n",num);
}

return 0;
}