题解

#include<bits/stdc++.h>
using namespace std;
int d[210],k[210];
int main(){
    int N,A,B;
    cin>>N>>A>>B;
    for(int i=1;i<=N;i++) cin>>k[i];
    memset(d,-1,sizeof(d));
    d[A]=0;
    queue<int> q;
    q.push(A);
    while(q.size()){
        int r=q.front();
        q.pop();
        if(r+k[r]<=N && d[r+k[r]]==-1){
	        d[r+k[r]]=d[r]+1;
                q.push(r+k[r]);
        }
        if(r-k[r]>=1 && d[r-k[r]]==-1){
		d[r-k[r]]=d[r]+1;
                q.push(r-k[r]);
        }
    }
    cout<<d[B];
    return 0;
}