C++ :

#include <iostream>
using namespace std;
#include <cstdio>
#include <cstring>
#include <cmath>
int n,a,b,t;
int ans=0x7f;
int edge[201][201];
int f[201][201];

int main()
{
	cin>>n>>a>>b;
	memset(edge,0x7f/2,sizeof(edge));
	memset(f,0x7f/2,sizeof(f));
	for (int i=1; i<=n; i++) 
	{
		f[i][i]=0;
	 	cin>>t;
	 	if (i+t<=n)
		{
			edge[i][i+t]=1;
	 		f[i][i+t]=edge[i][i+t];
	 	}
		if (i-t>=1)
		{
			edge[i][i-t]=1;
	 		f[i][i-t]=edge[i][i-t];
	 	}
	}
	for (int k=1; k<=n; k++)
	  for (int i=1; i<=n; i++)
	    if (i!=k)
	      for (int j=1; j<=n; j++)
	        if (i!=j&&j!=k)
	        {
	        	f[i][j]=min(f[i][j],f[i][k]+f[k][j]);
			}
	if (f[a][b]!=f[0][0]) cout<<f[a][b];
	else cout<<-1;
}

Python :

# coding=utf-8
import queue
def work():
    v=[False]*(n+1)
    if a==b:
        return 0
    q=queue.Queue()
    q.put( (0,a) )
    v[a]=True
    while not q.empty():
        t=q.get()
        for i in (1,-1):
            new_a=t[1]+c[t[1]]*i
            if 0<new_a<=n and not v[new_a]:
                if new_a==b:
                    return t[0]+1
                q.put( (t[0]+1,new_a) )
                v[new_a]=True
    return -1
        
    
n,a,b=map(int,input().split())
c=map(int,input().split())
c=[0]+list(c)
print(work())