题解 | #火车进站#

def xx(a, b, c):
    if not a and b:  # 只有进站
        return xx(a + b[:1], b[1:], c)
    if a and b:   #有进站和出站
        b1 = b.copy()  #注意列表的直接传递是会相互影响的 需要copy()
        return xx(a + b[:1], b[1:], c) + xx(a[:-1], b1, c + a[-1])
    if a and not b: #只有出站
        for i in a[::-1]:
            c += i
        return [c]


while True:
    try:
        n = int(input())
        b = input().split()
        for i in sorted(xx([], b, "")): 
            for j in i:
                print(j, end=" ")
            print("")
    except:
        break