a = [
    [1, 2, 3, 10],
    [4, 5, 6, 11],
    [7, 8, 9, 12]
]

column_number = len(a[0])
row_number = len(a)
position_idx = [0 for _ in range(row_number)]
break_flag = False    
permutations = list()

while (True):
    tmp = list()
    for row_idx, column_idx in enumerate(position_idx):
        tmp.append(a[row_idx][column_idx])
    permutations.append(tmp)
    
    # Switch positions
    position_idx[0] += 1
    for i, idx_value in enumerate(position_idx):
        if idx_value == column_number:
            if i == row_number - 1:
                break_flag = True
                break
            position_idx[i] = 0
            position_idx[i + 1] += 1
    
    if break_flag:
        break
print(len(permutations))
for i in permutations:
    print(i)