Increment an Arbitrary-Precision Integer Or Plus One

Given a non-empty array of digits representing a non-negative integer, increment one to the integer.

[1, 2, 3] => 123

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contains a single digit. You cannot use built-in functions such as int() and str().

SOLUTION: If you are going to solve this problem 3 edge cases should come into your mind.

Case 1: When there is no 9 digit in the array

Input: [1, 2, 3]

Output: [1, 2, 4]

Case 2: When the last element in the array is 9.

Input: [1, 2, 9]

Output: [1, 3, 0]                       Wrong Output: [1, 2, 10]        

Case 3: When all the elements in the array are 9.

Input: [9, 9, 9]

Output: [1, 0, 0 ,0]                 Wrong Output: [9, 9, 10] ,   [0, 0, 1] 

 

FINAL SOLUTION: