49分，求help

#include<bits/stdc++.h>
#include<queue>
using namespace std;
int main()
{
    int n;
    scanf("%d",&n);
    int l[5]={0,-1,1,0,0},r[5]={0,0,0,1,-1};
    queue<pair<int,int>> q;

    int farm[500][500]={0};
    int steps[500][500]={0};
    memset(farm,-1,sizeof(farm));
    memset(steps,-1,sizeof(steps));
    for(int i=1;i<=n;i++)
    {
        int x,y,t;
        scanf("%d%d%d",&x,&y,&t);

        for(int j=0;j<5;j++)
        {
            if(x+l[j]>=0&&y+r[j]>=0)
            {

            if(farm[x+l[j]][y+r[j]]==-1)farm[x+l[j]][y+r[j]]=t;
                else farm[x+l[j]][y+r[j]]=min(farm[x+l[j]][y+r[j]],t);
            }
        }
    }
   /* for(int i=0;i<=n;i++)
    {
        for(int j=0;j<=n;j++)printf("%d ",farm[i][j]);
        printf("\n");
    }*/

    q.push(make_pair(0,0));
    int num=1;
    steps[0][0]=0;
    while(!q.empty())
    {
        int x1=q.front().first,y1=q.front().second;
        q.pop();
        for(int j=1;j<5;j++)
        {
            if(x1+l[j]>=0&&y1+r[j]>=0)
                if(farm[x1+l[j]][y1+r[j]]>x1+l[j]+y1+r[j]&&steps[x1+l[j]][y1+r[j]]==-1||farm[x1+l[j]][y1+r[j]]==-1)
                {
                    q.push(make_pair(x1+l[j],y1+r[j]));
                    steps[x1+l[j]][y1+r[j]]=steps[x1][y1]+1;
                }
        }
        if(farm[x1][y1]==-1)
        {
            num=0;
            printf("%d",steps[x1][y1]);
            break;
        }
     //   printf("%d %d\n",x1,y1);
    }
    if(num==1) printf("-1");
    return 0;
}