题解

#include <bits/stdc++.h>
using namespace std;
const int N=209;
int n,x,y;
int f[N];
bool ok[N];
int k[N];
void bfs()
{
    queue<int> q;
    q.push(x);
    ok[x]=1;
    f[x]=0;
    while(!q.empty())
    {
        int now=q.front();
        q.pop();
        int z=now+k[now];
        if(z<=n&&!ok[z])
        {
            q.push(z);
            ok[z]=1;
            f[z]=f[now]+1;
            if(z==y)
            {
                return;
            }
        }
        z=now-k[now];
        if(z>=1&&!ok[z])
        {
            q.push(z);
            ok[z]=1;
            f[z]=f[now]+1;
            if(z==y)
            {
                return;
            }
        }
    }
}
int main()
{
    cin>>n>>x>>y;
    for(int i=1;i<=n;i++)
    {
		cin>>k[i];
    }
    bfs();
    if(ok[y]!=0)
    {
        cout<<f[y]<<endl;
    }
    else
    {
        cout<<-1<<endl;
    }
    return 0;
}