对n个不同正数进行排列，一共有多少种排列方式

import java.util.Scanner;

public class NumberGroup {

	public static void main(String[] args) {

		System.out.println("请输入一个正数");
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] a = new int[n];
		int[] b = new int[a.length];
		System.out.println("请输入"+ n +"个正数");
		for(int i=0; i<a.length; i++) {
			a[i] = scan.nextInt();
		}
		
		for(int i=0; i<a.length; i++) {		
			numberGroup(a[0], a, 0, b);

		}
		
	}

	public static void numberGroup(int num, int[] a, int count, int[] b) {
		b[count] = num;
		count++;

		if (count >= a.length) {                             //递归的出口
			for (int i = 0; i < b.length; i++) {
				System.out.print(b[i] + " ");
				if (i == b.length - 1)
					System.out.println();
			}

			// b[count - 1] = 0;
			return;
		}

		for (int i = 0; i < a.length; i++) {
			if (!jiancha(b, a[i])) {
				numberGroup(a[i], a, count, b);
				qingchu(count, b);                                      //关键
			}
		}

	}

	public static boolean jiancha(int[] b, int x) {
		for (int i = 0; i < b.length; i++) {
			if (b[i] == x) {
				return true;
			}
		}
		return false;
	}

	public static void qingchu(int count, int[] b) {

		for (int j = count; j < b.length; j++) {
			b[j] = 0;
		}

	}

}