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What difficulty level is this coding question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Apple.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Apple during technical interviews.

Zero out duplicates and sort an array

Company: Apple

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

## Coding question You are given an integer array `arr` of length about **75**. - The data is **not sorted**. - The array may contain **duplicate values**. - You must **zero out duplicates** and then **sort** the array. - Try to keep **time and space complexity** in mind. - **Do not use** built-in/native sorting utilities (e.g., `sort()`), and do not call library implementations of quicksort/bubblesort/etc. ### Clarification to assume (if not specified) If a value appears multiple times, **keep exactly one occurrence** and replace all other occurrences with **0**. Then sort the entire array in **non-decreasing** order. ### Input - An integer array `arr`. ### Output - Return the transformed array after (1) zeroing duplicate occurrences and (2) sorting. ### Example - Input: `[3, 1, 3, 2, 2]` - After zeroing duplicates (keeping first occurrence): `[3, 1, 0, 2, 0]` - After sorting: `[0, 0, 1, 2, 3]`

Quick Answer: This question evaluates proficiency in array manipulation, duplicate handling, and custom sorting logic with attention to time and space complexity, and it falls within the Coding & Algorithms domain.

You are given an integer array arr. Traverse the array from left to right and keep the first occurrence of each value. Every later occurrence of the same value must be replaced with 0. After that, sort the entire resulting array in non-decreasing order and return it. Do not use built-in sorting utilities such as sort() or sorted(); implement the sorting yourself. Note: if the duplicated value is 0, replacing it with 0 does not change its appearance, but it is still considered a duplicate occurrence.

Constraints

0 <= len(arr) <= 100000; the interview version often uses arrays of around 75 elements
-1000000000 <= arr[i] <= 1000000000
Keep the first occurrence of each value and replace every later duplicate with 0
Do not use built-in/native sorting utilities

Examples

Input: ([3, 1, 3, 2, 2],)

Expected Output: [0, 0, 1, 2, 3]

Explanation: Keep the first 3 and first 2, replace later duplicates with 0 to get [3, 1, 0, 2, 0], then sort.

Input: ([],)

Expected Output: []

Explanation: An empty array stays empty.

Input: ([4],)

Expected Output: [4]

Explanation: A single element has no duplicates, so the array is unchanged after sorting.

Input: ([4, 4, 4, 4],)

Expected Output: [0, 0, 0, 4]

Explanation: Only the first 4 is kept; the other three become 0, then the array is sorted.

Input: ([-1, 3, -1, 2, 3],)

Expected Output: [-1, 0, 0, 2, 3]

Explanation: After zeroing later -1 and 3 values, the array becomes [-1, 3, 0, 2, 0], which sorts to [-1, 0, 0, 2, 3].

Input: ([0, 2, 0, 2, 1],)

Expected Output: [0, 0, 0, 1, 2]

Explanation: Keep the first 0 and first 2. Later 0 and 2 are duplicates and become 0, giving [0, 2, 0, 0, 1], then sort.

Input: ([5, 3, 4, 1, 2],)

Expected Output: [1, 2, 3, 4, 5]

Explanation: All values are unique, so the task reduces to sorting the array without built-in sort utilities.

Hints

Use a hash set while scanning from left to right to decide whether a value has already appeared.
Once the array is transformed, implement an O(n log n) sorting algorithm yourself, such as merge sort.

Quick Overview

This question evaluates proficiency in array manipulation, duplicate handling, and custom sorting logic with attention to time and space complexity, and it falls within the Coding & Algorithms domain.