Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
You may assume the integer do not contain any leading zero, except the number 0 itself.
The digits are stored such that the most significant digit is at the head of the list.
What the question really means
|[2, 3, 5]||[2, 3, 6]|
|[9, 9]||[1, 0, 0]|
- Loop through the given array from tail
- If the current digit is less than 9, add 1 and return
- If the current digit is 9, set it to 0
to the head of the array and return