LC066 - Plus One

Problem

You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's.

Increment the large integer by one and return the resulting array of digits.

Solution

Naive

def plusOne(self, digits: List[int]) -> List[int]:
	if digits[-1] < 9:
		digits[-1] += 1
	else:
		carry = True
		# iterate each digit from the last digit

		for i in range(len(digits)-1, -1, -1):
			# add carry
			if carry:
				digits[i] += 1

			if digits[i] >= 10:
				carry = True
				digits[i] -= 10

		else:
			carry = False
			break

# add to start of list if carry remains

	if carry:
		digits.insert(0, 1)

	return digits