代码：

#include<bits/stdc++.h>
using namespace std;

int M[201];
int n, a, b;
int k[201];
queue<int> q;

int main(){
	cin >> n >> a >> b;
	for(int i=1; i<=n; i++) cin >> k[i];
	memset(M, -1, sizeof(M));
	M[a] = 0;

	q.push(a);
	while(!q.empty()){
		int p = q.front();
		q.pop();
		if(p==b) break;
		if(p+k[p]<=n) {
			M[p+k[p]] = M[p]+1;
			q.push(p+k[p]);
		}
		if(p-k[p]>=1) {
			M[p-k[p]] = M[p]+1;
			q.push(p-k[p]);
		}
	}

	cout << M[b] << endl;

	system("pause");
	return 0;
}

测试点