Array Questions at Hashedin: What to Expect

Array questions dominate Hashedin's technical interviews, making up 24 of their 32 most frequently asked problems. This focus isn't arbitrary. Arrays are the fundamental data structure for representing sequential data, and questions about them efficiently test a candidate's core algorithmic thinking, ability to handle edge cases, and skill in writing clean, optimized code under time pressure. Mastering array problems is the single most impactful preparation you can do for a Hashedin interview.

What to Expect — Types of Problems

Hashedin's array problems test a wide range of concepts, but they cluster around a few key patterns. Expect heavy emphasis on two-pointer techniques for problems involving sorted arrays, pair sums, or removing duplicates. Sliding window problems are common for finding subarrays with specific properties, like maximum sum or shortest length meeting a condition. You will also encounter in-place array manipulation, which tests your ability to modify an array without using extra space, often using clever swapping or overwriting strategies. Finally, prefix sum and hashing patterns appear frequently for problems involving subarray sums or finding specific elements. The difficulty often lies not in complex data structures, but in applying these fundamental patterns optimally.

How to Prepare — Study Tips with One Code Example

Focus on pattern recognition, not memorization. For each problem, identify the core pattern before writing code. Practice drawing out the array and stepping through your algorithm with sample inputs and edge cases (empty array, single element, all duplicates, negative numbers). Time yourself to build speed.

A critical pattern is the two-pointer technique for in-place removal. Consider the problem: "Given a sorted array, remove duplicates in-place such that each element appears only once and return the new length."

The efficient approach uses a slow pointer to track the position of the last unique element and a fast pointer to scan ahead.

def removeDuplicates(nums):
    if not nums:
        return 0
    slow = 0
    for fast in range(1, len(nums)):
        if nums[fast] != nums[slow]:
            slow += 1
            nums[slow] = nums[fast]
    return slow + 1

Recommended Practice Order

Tackle problems in a logical progression to build confidence. Start with basic traversal and in-place operations (e.g., remove element, merge sorted arrays). Next, master two-pointer techniques for sorted arrays. Then, move to sliding window problems for subarrays. After that, practice prefix sum and hashing applications. Finally, combine patterns for more complex challenges, like problems involving rotation or next permutation. Solve all 24 Hashedin array questions in this order, ensuring you can implement each solution from scratch without hints.

Practice Array at Hashedin