poj3669 Meteor Shower(bfs java)

package bfs;

/**
* Created by user on 2017/10/17.
*/

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

/**
* Created by user on 2017/8/9.
*/
public class poj3669 {
static int MAX_N=400+2;
static int map[][]=new int[MAX_N][MAX_N];
static int m,mx,my,t;
static  int dir[][]={{-1,0},{0,1},{1,0},{0,-1}};
static boolean vis[][]=new boolean[MAX_N][MAX_N];
static int INF=100000000;
class Node{
int x;int y;int step;
}
static poj3669 poj=new poj3669();

public  static void main(String args[]){
Scanner scanner=new Scanner(System.in);
m=scanner.nextInt();
init();
for(int i=0;i<m;i++){
mx=scanner.nextInt();
my=scanner.nextInt();
t=scanner.nextInt();
if (map[mx][my]==INF){
map[mx][my]=t;
}
for(int j=0;j<4;j++){
int dx=mx+dir[j][0];
int dy=my+dir[j][1];
if(check(dx,dy)&&(map[dx][dy]>t||map[dx][dy]==INF)){
map[dx][dy]=t;
}
}

}
int count=bfs(0,0,0);
System.out.println(count);
}

private static int bfs(int x, int y, int ans) {
if(map[x][y]==0){
return -1;
}
Queue<Node> queue;queue=new LinkedList<Node>();
if(!queue.isEmpty()){
queue.clear();
}
vis[x][y]=true;
Node first=poj.new Node();
first.x=x;
first.y=y;
first.step=ans;
queue.offer(first);
while(queue.size()!=0){
Node from=queue.poll();
int sx=from.x,sy=from.y;
if(map[sx][sy]==INF){
return from.step;
}
for(int i=0;i<4;i++){
int dx=sx+dir[i][0];
int dy=sy+dir[i][1];
if(check(dx,dy)&&!vis[dx][dy]&&(from.step+1<map[dx][dy]||map[dx][dy]==INF)){
vis[dx][dy]=true;
Node to=poj.new Node();
to.x=dx;
to.y=dy;
to.step=from.step+1;
queue.offer(to);
}
}
}
return -1;
}

private static boolean check(int dx, int dy) {
if(dx>=0&&dy>=0){
return true;
}
return false;
}

public static void init(){
for(int i=0;i<MAX_N;i++){
for(int j=0;j<MAX_N;j++){
map[i][j]=INF;
}
}
}
}