plus_one.py

"""
Given a non-negative number represented as an array of digits,
plus one to the number.

The digits are stored such that the most significant
digit is at the head of the list.
"""


def plus_one_v1(digits):
    """
    :type digits: List[int]
    :rtype: List[int]
    """
    digits[-1] = digits[-1] + 1
    res = []
    ten = 0
    i = len(digits)-1
    while i >= 0 or ten == 1:
        summ = 0
        if i >= 0:
            summ += digits[i]
        if ten:
            summ += 1
        res.append(summ % 10)
        ten = summ // 10
        i -= 1
    return res[::-1]


def plus_one_v2(digits):
    n = len(digits)
    for i in range(n-1, -1, -1):
        if digits[i] < 9:
            digits[i] += 1
            return digits
        digits[i] = 0
    digits.insert(0, 1)
    return digits


def plus_one_v3(num_arr):

    for idx, digit in reversed(list(enumerate(num_arr))):
        num_arr[idx] = (num_arr[idx] + 1) % 10
        if num_arr[idx]:
            return num_arr
    return [1] + num_arr