Array Algorithms for Interviews: What to Learn & How to Practice

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What array algorithms and problem-solving patterns should you learn, and how can you practice them effectively?
Share useful resources, strategies, and tips to help others prepare for array-based interview questions.

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Arrays are where most interview prep starts because a handful of patterns cover a huge chunk of problems.

Once you know two pointers, sliding window, prefix sums, and binary search on sorted arrays, you can pattern match new problems fast instead of starting from scratch every time. The trap most people fall into is grinding random problems without noticing the repeated shape underneath them.

Practice works best when you group problems by pattern instead of solving randomly, and when you force yourself to explain the approach out loud before coding it.

  • Learn two pointers, sliding window, prefix sum, and binary search first
  • Practice on LeetCode (filter by pattern, not difficulty alone) and NeetCode 150 for a curated roadmap
  • Use Blind 75 (a shortlist of 75 must-do interview problems) as a tight list if you’re short on time
  • Explain your approach out loud before coding, and revisit old solved problems after a week
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Start with common array patterns like two pointers, sliding window, prefix sums, sorting, binary search, and hash maps. Practice topic by topic instead of randomly. GUVI’s CodeKata is a useful platform for hands-on practice, with dedicated array problems and challenges for interview preparation. You can also use LeetCode, HackerRank, and GeeksforGeeks to practice more. The key is to understand the pattern behind each solution and revisit problems you struggled with.

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Start with the basics like searching, sorting, two pointers, sliding window, prefix sums, and hashing. Once you’re comfortable with those, practice common patterns like finding duplicates, subarrays, and pair-sum problems.

For practice, pick problems from LeetCode, GeeksforGeeks, or HackerRank and solve a few consistently instead of trying to finish hundreds at once. Also, don’t just memorize solutions understand why the approach works and try solving the same problem in a different way. That makes interview questions much easier to handle.

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For array algorithms for interviews, the best approach is to learn a small set of reusable problem-solving patterns instead of memorising dozens of solutions. Arrays appear in almost every DSA interview because they test indexing, time complexity, searching, sorting, hashing, and optimisation skills.

Array Algorithms and Patterns to Learn

Start with these core patterns:

  • Array traversal: Iterating, counting, finding minimum/maximum, and in-place updates.
  • Two pointers: Useful for sorted arrays, pair-sum problems, removing duplicates, and partitioning.
  • Sliding window: Ideal for maximum/minimum subarray, substring, and fixed or variable window problems.
  • Prefix sums: Helps answer range-sum queries and optimise repeated subarray calculations.
  • Hashing and frequency maps: Useful for Two Sum, duplicate detection, frequency counting, and lookup-based problems.
  • Sorting: Learn merge sort, quicksort concepts, custom sorting, and when sorting simplifies a problem.
  • Binary search: Practice standard search, lower/upper bounds, rotated arrays, and binary search on the answer.
  • Kadane’s algorithm: Essential for maximum subarray sum problems.
  • Intervals: Learn merging intervals, overlapping ranges, and scheduling-style problems.
  • Matrix traversal: Practice row/column traversal, spiral matrices, rotation, and grid-based array questions.

How to Practise Array Problems Effectively

A good DSA interview preparation strategy is to practise by pattern rather than randomly selecting questions.

  1. Understand the brute-force approach first.
  2. Calculate its time and space complexity.
  3. Identify the repeated work causing inefficiency.
  4. Look for a suitable pattern such as hashing, sliding window, or two pointers.
  5. Write the optimised solution without referring to notes.
  6. Revisit the same problem after a few days.

For example, a nested-loop solution running in O(n²) may often be improved to O(n) using a HashMap, prefix sum, or sliding window.

Best Array Problems to Practise

Beginners should cover problems such as:

  • Two Sum
  • Best Time to Buy and Sell Stock
  • Maximum Subarray
  • Move Zeroes
  • Remove Duplicates From Sorted Array
  • Product of Array Except Self
  • Maximum Sum Subarray
  • Merge Intervals
  • Search in Rotated Sorted Array
  • Container With Most Water

Platforms such as LeetCode, HackerRank, GeeksforGeeks, and NeetCode are useful for structured array interview practice.

The goal is not to solve hundreds of array questions. Focus on recognising the underlying pattern quickly and explaining why a solution works, its complexity, and what trade-offs it makes. That skill is far more valuable in coding interviews than memorising solutions.