static int count = 0;

	public static void main(String[] args) {
		char[] a = { ‘1‘, ‘2‘, ‘3‘, ‘4‘ };
		boolean h[] = new boolean[100];
		int n = 3;
		char[] b = new char[n];
		fun(a, 0, n, b, h);
		System.out.println(count);
	}
	// k是b数组大小， n选择几个数， h标记b里有没有。
	static void fun(char a[], int k, int n, char b[], boolean h[]) {
		if (k == n) {
			f(b, 0);
		} else if (k < n) {
			for (int i = k; i < a.length; i++) {
				if (!h[i]) {
					b[k] = a[i];
					h[i] = true;
				} else {
					break;
				}
				fun(a, k + 1, n, b, h);
				h[i] = false;
			}
		} else
			return;
	}

	static void f(char a[], int n) {
		if (a.length == n) {
			System.out.println(a);
			count++;
		} else {
			for (int i = n; i < a.length; i++) {
				char c = a[n];
				a[n] = a[i];
				a[i] = c;
				f(a, n + 1);
				c = a[n];
				a[n] = a[i];
				a[i] = c;
			}
		}

	}