poj 2706 java

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

public class Main {

public static final int a[][] = {{-2,-1},{-2,1},{-1,2},{1,2},{2,1},{2,-1},{1,-2},{-1,-2}};
static int n ;
public static final int sx0[][] = {{-2,0},{-2,1},{-1,0},{-1,1},{-1,0},{-1,-1},{-1,1},{-1,1},{-2,2}};
public static final int sy0[][] = {{0,1},{0,2},{1,1},{1,2},{0,2},{0,1},{0,3},{1,0},{0,1}};

public static final int sx1[][] = {{0,1},{0,2},{1,1},{1,2},{-1,1},{0,1},{1,1},{0,-1},{1,0}};
public static final int sy1[][] = {{1,-1},{1,0},{2,-1},{2,0},{1,0},{2,0},{3,0},{1,1},{2,2}};

public static final int s[][] = {{-1,-1},{-1,1},{1,1},{-1,1},{1,1},{1,-1},{-1,-1},{1,-1}};

static int cx[] ;
static int cy[] ;

public static void main(String[] args) {

Scanner scan = new Scanner(System.in);

while(true){
n = scan.nextInt();
int m = scan.nextInt();

if(n == 0&& m==0)
break;

cx = new int[m];
cy = new int[m];
boolean link[][] = new boolean[m][m];
int map[][] = new int[n+1][n+1];
for(int i=0;i<=n;i++)
java.util.Arrays.fill(map[i], -1);

for(int d=0;d<m;d++){
int y = scan.nextInt();
int x = scan.nextInt();
map[x][y] = d;
cx[d] = x;
cy[d] = y;
drawLine(link,map,x,y);

}

boolean flag1 = false;
boolean flag2 = false;
for(int i=0;i<=n;i++){
if(map[i][0]%2==0&&bfs(map[i][0],link,m)){
flag1 = true;
break;
}
}
if(!flag1){
System.out.println("no");
continue;
}

for(int i=0;i<=n;i++){
if(map[i][0]%2==0&&map[i][0]!=m-1&&bfs(map[i][0],link,m-1)){
flag2 = true;
break;
}
}
if(flag2)
System.out.println("no");
else
System.out.println("yes");

}

}

public static boolean bfs(int v,boolean[][] link,int m) {

Queue<Integer> q = new LinkedList<Integer>();
q.add(v);
boolean visit[] = new boolean[m];
visit[v] = true;
while(!q.isEmpty()){
v = q.poll();
for(int i=0;i<m;i++){
if(!visit[i]&&link[v][i]){
if(cy[i]==n)
return true;
q.add(i);
visit[i] = true;
}
}
}

return false;
}

public static void drawLine(boolean[][] link, int[][] map,int xs,int ys) {

for(int i=0;i<8;i++){

int x = xs + a[i][0];
int y = ys + a[i][1];

if(x>=0&&x<=n&&y>=0&&y<=n&&map[x][y]%2==map[xs][ys]%2&&!link[map[x][y]][map[xs][ys]]){

if(i==2||i==3||i==6||i==7){
int k ;
for(k=0;k<9;k++){
int xa = xs + s[i][0]*sx0[k][0];
int ya = ys + s[i][1]*sx0[k][1];

int xb = xs + s[i][0]*sy0[k][0];
int yb = ys + s[i][1]*sy0[k][1];
if(check(xa,ya)&&check(xb,yb)&&map[xa][ya]!=-1&&map[xb][yb]!=-1&&link[map[xa][ya]][map[xb][yb]]){
break;
}
}
if( k == 9){
link [map[x][y]][map[xs][ys]] = true;
link [map[xs][ys]][map[x][y]] = true;
}

}else{
int k ;
for(k=0;k<9;k++){
int xa = xs + s[i][0]*sx1[k][0];
int ya = ys + s[i][1]*sx1[k][1];

int xb = xs + s[i][0]*sy1[k][0];
int yb = ys + s[i][1]*sy1[k][1];
if(check(xa,ya)&&check(xb,yb)&&map[xa][ya]!=-1&&map[xb][yb]!=-1&&link[map[xa][ya]][map[xb][yb]]){
break;
}
}
if( k == 9){
link [map[x][y]][map[xs][ys]] = true;
link [map[xs][ys]][map[x][y]] = true;
}

}

}

}

}

public static boolean check(int a, int b) {

return a>=0&&b>=0&&a<=n&&b<=n;
}
}