Increment a large integer represented as an array of digits.
O(n)
O(1)
def plusOne(digits): digits = digits[::-1] one, i = 1, 0 while one: if i < len(digits): if digits[i] == 9: digits[i] = 0 else: digits[i] += 1 one = 0 else: digits.append(1) one = 0 i += 1 return digits[::-1]