HDU1548(楼梯问题bfs)

#include"cstdio"
#include"queue"
#include"cstring"
using namespace std;
const int MAXN=;
typedef pair<int,int> P;
int N,A,B;
int K[MAXN];
int vis[MAXN];
int bfs()
{
    queue<P> que;
    que.push(P(,A));
    vis[A]=;
    while(!que.empty())
    {
        P now=que.front();que.pop();
        if(now.second==B)
        {
            return now.first;
        }
        for(int i=-;i<=;i++)
        {
            int next=now.second+K[now.second]*i;
            if(<next&&next<=N&&!vis[next])
            {
                vis[next]=;
                que.push(P(now.first+,next));
            }
        }
    }
    return -;
}
int main()
{
    while(scanf("%d",&N)!=EOF&&N!=)
    {
        scanf("%d %d",&A,&B);
        for(int i=;i<=N;i++)
        {
            scanf("%d",&K[i]);
        }
        memset(vis,,sizeof(vis));
        printf("%d\n",bfs());
    }
    return ;
}