AI & Technical question

Write a code to increment an array of digits (0 to 9).

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What this question tests

Tests basic coding fluency expected of a technical PM: writing a correct, simple algorithm and explaining edge cases in plain terms.

Clarify the input: an array of digits representing a number, most significant digit first, and the output should be the array after adding one.
Walk through the logic: start from the last digit, add one, and if it is less than 10, return immediately since no carry is needed.
Handle the carry case: if a digit becomes 10, set it to 0 and carry one to the digit before it, repeating leftward.
Handle the edge case: if every digit carries (all 9s, like 999), the array grows by one digit with a leading 1.
Write the code in simple pseudocode or a language like Python, iterating from the end of the array.

Handles the carry-propagation case correctly, since a naive solution that only increments the last digit fails on inputs like 9 or 99.
Explicitly calls out the all-9s edge case (999 becomes 1000), which requires growing the array, a common trap in this exact problem.
Explains the logic in plain language before or alongside the code, which matters for a PM-level technical assessment.
Keeps the solution simple and iterative rather than overcomplicating with unnecessary recursion or libraries.

Forgetting the carry case entirely and only incrementing the last digit.
Missing the edge case where all digits are 9 and the array needs to grow by one element.

Chapters of the AI PM course that teach what this question tests.