拉斯维加斯和回溯法解N皇后问题

[雪花神剑]

package artificial;

import java.util.Random;
import java.util.Scanner;

public class LVQueen {
int n;
int[] x;
int[] y;

boolean place(int k){
for(int j=1;j<k;j++){
if((Math.abs(k-j)==Math.abs(x[j]-x[k]))||(x[j]==x[k]))
return false;
}
return true;
}
boolean backtrack(int t){
if(t>n){
for(int i=1;i<=n;i++)y[i]=x[i];
return true;
}
else{
for(int i=1;i<=n;i++){
x[t]=i;
if(place(t)&&backtrack(t+1))
return true;
}
return false;
}
}
boolean queenLV(int stepVegas){
Random rand=new Random();
int k=1;
int count=1;
while((k<=stepVegas)&&(count>0)){
count=0;
for(int i=1;i<=n;i++){
x[k]=i;
if(place(k))y[count++]=i;
}
System.out.println("count="+count);
if(count>0)x[k++]=y[rand.nextInt(count)];
}
return (count>0);
}
boolean nQueen(int n){
System.out.println(n);
x=new int[n+1];
y=new int[n+1];
for(int i=0;i<=n;i++){
x[i]=0;
y[i]=0;
}
int stop=2;//允许随机放置的皇后数
boolean found=false;
while(!queenLV(stop));//反复调用拉斯维加斯算法，直到找到解
System.out.println("循环结束");
if(backtrack(stop+1)){
for(int i=1;i<=n;i++){
System.out.print("("+i+","+x[i]+")");
found=true;
}
}
return found;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner scan=new Scanner(System.in);
int n=scan.nextInt();
long startTime=System.currentTimeMillis();
LVQueen lq=new LVQueen();
lq.nQueen(n);
long endTime=System.currentTimeMillis();
System.out.println("用时："+(endTime-startTime)+"毫秒");

}
}
请各位高手看看，程序运行时语句 while(!queenLV(stop));无法结束，一直打印count=0,进入死循环。