Python/data_structures/stacks/lexicographical_numbers.py

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from collections.abc import Iterator
def lexical_order(max_number: int) -> Iterator[int]:
"""
Generate numbers in lexical order from 1 to max_number.
>>> " ".join(map(str, lexical_order(13)))
'1 10 11 12 13 2 3 4 5 6 7 8 9'
>>> list(lexical_order(1))
[1]
>>> " ".join(map(str, lexical_order(20)))
'1 10 11 12 13 14 15 16 17 18 19 2 20 3 4 5 6 7 8 9'
>>> " ".join(map(str, lexical_order(25)))
'1 10 11 12 13 14 15 16 17 18 19 2 20 21 22 23 24 25 3 4 5 6 7 8 9'
>>> list(lexical_order(12))
[1, 10, 11, 12, 2, 3, 4, 5, 6, 7, 8, 9]
"""
stack = [1]
while stack:
num = stack.pop()
if num > max_number:
continue
yield num
if (num % 10) != 9:
stack.append(num + 1)
stack.append(num * 10)
if __name__ == "__main__":
from doctest import testmod
testmod()
print(f"Numbers from 1 to 25 in lexical order: {list(lexical_order(26))}")