66. plus one

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.

solutions

This is the manual addition solution.

def plusOne(self, digits: List[int]) -> List[int]:
	carry = 1
	ptr = len(digits)-1
	  
	while ptr >= 0:
		if carry == 0:
			break
		if carry == 1:
			digits[ptr] += 1
	  
		if digits[ptr] > 9:
			digits[ptr] -= 10
			carry = 1
		else:
			carry = 0
	  
		ptr -= 1
 
	# edge case for something like 99
	if carry == 1:
		digits = [1] + digits
	
	return digits

Tip

We could also just convert the digits to an int, add 1, and then convert it back to a list of digits.