代码求助

#include<bits/stdc++.h>
using namespace std;
const int N=3e2+5;
int m;
int down[N][N],ans[N][N];
int dx[4]={0,0,-1,1};
int dy[4]={1,-1,0,0};
bool check(int x,int y)
{
	if(x<0||y<0||x>N||y>N)return 1;
	return 0;
}
void add(int x,int y,int t)
{
	if(check(x,y))return;
	down[x][y]=min(down[x][y],t);
	for(int i=0;i<4;i++)
	{
		int xx=x+dx[i];
		int yy=y+dy[i];
		if(check(xx,yy))continue;
		down[xx][yy]=min(down[xx][yy],t);
	}
}
int bfs(int sx,int sy)
{	
	bool vis[N][N];
	memset(vis,0,sizeof(vis));
	vis[sx][sy]=1;
	queue<pair<int,int> >que;
	que.push(make_pair(sx,sy));
	ans[sx][sy]=0;
	while(que.size())
	{
		int x=que.front().first;
		int y=que.front().second;
		que.pop();
		//if(down[x][y]>=0x3f3f)
		for(int i=0;i<4;i++)
		{
			int xx=x+dx[i];
			int yy=y+dy[i];
			if(check(xx,yy)||vis[xx][yy])continue;
			if(ans[x][y]+1>=down[xx][yy])continue;
			vis[xx][yy]=1;
			ans[xx][yy]=ans[x][y]+1;
			que.push(make_pair(xx,yy));
		}
	}
	int ansx=1e9;
	for(int i=1;i<=N;i++)
	{
		for(int j=1;j<=N;j++)
		{
			if(down[i][j]>1000&&ans[i][j]!=-1)ansx=min(ansx,ans[i][j]);
			//cout<<ans[i][j]<<" ";
		}
		//cout<<endl;
	}
	if(ansx==1e9)return -1;
	return ansx;
}
int main()
{
	ios::sync_with_stdio(false);
	cin>>m;
	memset(down,0x3f3f,sizeof(down));
	memset(ans,-1,sizeof(ans));
	for(int i=1;i<=m;i++)
	{
		int x,y,t;
		cin>>x>>y>>t;
		add(x,y,t);
	}
	cout<<bfs(0,0);
	
	return 0;
}