2,4wa了，7，10tle，萌新求助

#include <cstdio>
#include <queue>
#include <algorithm>
#include <iostream>
using namespace std;
int n,A,B,vis[2100]={0},k[2100];
struct node
{
	int num,step;	
};
int inmap(int x)
{
	return x<=n&&x>=1;
}
void BFS(int A,int B)
{
	int i;
	vis[A]=1;
	queue<node> q;
	q.push({A,0});
	while(!q.empty())
	{
		node now=q.front();
		if(now.num==B)
		{
			printf("%d",now.step);
			return;
		}
		i=now.num;
			if(inmap(now.num+k[i])&&(!vis[now.num+k[i]]||k[now.num]!=k[now.num+k[i]]))
			{
				vis[now.num+k[i]]=1;
				q.push({now.num+k[i],now.step+1});
			}
			if(inmap(now.num-k[i])&&(!vis[now.num-k[i]]||k[now.num]!=k[now.num-k[i]]))
			{
				vis[now.num-k[i]]=1;
				q.push({now.num-k[i],now.step+1});
			}
		q.pop();
	}
}
int main()
{
	int i;
	scanf("%d%d%d",&n,&A,&B);
	for(i=1;i<=n;i++)
	{
		scanf("%d",&k[i]);
	}
	BFS(A,B);
	return 0;
}