浣熊隧道（bfs + queue）

#include<bits/stdc++.h>
using namespace std;
int n,a,b;
int mp[10001],minst=9999,vis[10001];
struct node{
	int pos,step;
};
bool inmp(int pos){
	return pos>=1 and pos<=n;
}
void bfs(){
	queue<node> q;
	q.push({a,0});
	while(q.size()){
		node s=q.front();
		q.pop();
		int dep=s.pos,st=s.step;
		if(dep==b){
			minst=min(minst,st);
			return ;
		}
		int n1=dep+mp[dep],n2=dep-mp[dep];
		if(inmp(n1) and !vis[n1]){
			q.push({n1,st+1});
			vis[n1]=1;
		}
		if(inmp(n2) and !vis[n2]){
			q.push({n2,st+1});
			vis[n2]=1;
		}
	}
	return ;
}
int main(){
	cin>>n>>a>>b;
	for(int i=1;i<=n;i++) cin>>mp[i];
	bfs();
	if(minst==9999) cout<<-1;
	else cout<<minst;
	return 0;
}