根据入栈序列输出所有可能的出栈序列

    public class Main {
        private static int number;

    	public static void main(String[] args) {
    		Scanner cin = new Scanner(System.in);
    		int T = cin.nextInt();
    		int[] A = new int[T];
    		int k = 0;
    		while (T-- > 0) {
    			A[k++] = cin.nextInt();
    		}
    		int[] count = { 0, 0 };// count[0]: 进栈的次数；count[1]:出栈的次数
    		ArrayList<Integer> stack = new ArrayList<Integer>();
    		func(stack, count, k, A);
    		System.out.println(number);
    		cin.close();
    	}
    
    	public static void func(List<Integer> stack, int[] count, int n, int[] A) {
    		// 1代表进栈；0代表出栈
    		if (count[0] < n) {
    			stack.add(1);
    			count[0]++;
    			func(stack, count, n, A);
    			count[0]--;
    			stack.remove(stack.size() - 1);
    		}
    
    		if (count[1] < count[0]) {
    			stack.add(0);
    			count[1]++;
    			func(stack, count, n, A);
    			count[1]--;
    			stack.remove(stack.size() - 1);
    		}
    
    		if (stack.size() == 2 * n) {
    			Iterator<Integer> it = stack.iterator();
    			Stack<Integer> stk = new Stack<Integer>();
    			int j = 0;
    			while (it.hasNext()) {
    				int out = it.next();
    				if (out == 1) {
    					stk.push(A[j++]);
    				} else {
    					System.out.print(stk.pop() + " ");
    				}
    			}
    			number++;
    			System.out.println();
    		}
    	}
    }