原题： https://www.luogu.com.cn/problem/P1135

#include<bits/stdc++.h>
using namespace std;
const int N = 500;
int n,a,b;
int flood[N];
int d[N];

int bfs(int n,int a,int b)
{
    queue<int>q;
    memset(d,-1,sizeof(d));
    q.push(a);
    d[a]=0;

    while(!q.empty())
    {
        auto t = q.front();
        q.pop();

        int up =t +flood[t];
            if(d[up]==-1 and up>0 and up<=n)
            {
                d[up] = d[t]+1;
                q.push({up});
            }
        int down = t-flood[t];
            if(d[down]==-1 and down>0 and down<=n)
            {
                d[down] = d[t]+1;
                q.push({down});
            }
    }
    return d[b];
}





int main()
{
    cin>>n>>a>>b;
    for(int i=1;i<=n;i++)
    {
        cin>>flood[i];
    }

    cout<<bfs(n,a,b);


    return 0;
}