def isLucky(t):
    s0 = 0; s1 = 0
    n = len(t)
    k = n//2
    for i in range(k):
        s0 += t[i]
    for i in range(k, n):
        s1 += t[i]
    ### if s0 == s1:
    ###     return True
    ### else:
    ###     return False
    return s0 == s1
    
def nextTicket(t):
    '''Change list jf digits t to the next list 
       in the lexicographic order'''
    i = len(t) - 1
    while i >= 0:
        if t[i] < 9:
            t[i] += 1
            return True
        t[i] = 0
        i -= 1
    return False
    
def printLuckyTickets(n):
    t = [0]*n
    while True:
        if isLucky(t):
            print(t)
        if not nextTicket(t):
            break

def luckyTickets(n):
    '''Return the list of lucky tickets of length n'''
    res = []
    t = [0]*n
    while True:
        if isLucky(t):
            res.append(t.copy())
        if not nextTicket(t):
            break
    return res
    
def numLuckyTickets(n):
    numLucky = 0
    t = [0]*n
    while True:
        if isLucky(t):
            numLucky += 1
        if not nextTicket(t):
            break
    return numLucky