Let's understand how Arrays & Strings can be asked in coding interviews

Arrays and strings are the building blocks of most coding interview problems. They test your logic, optimization skills, and your ability to recognize patterns — and they pop up in everything from system design to algorithm rounds.

*1.1. Rotation*

You may be asked to rotate an array left or right by k positions, in-place and with O(1) space.

Example:

> Rotate [1, 2, 3, 4, 5] right by 2 → Output: [4, 5, 1, 2, 3]

It tests how well you manage array indices and edge cases like k > n.

*1.2. Sliding Window*

Used to reduce brute-force O(n²) solutions to O(n). Interviewers love this for problems around subarrays, substrings, or fixed windows.

*Example* :

> Find the max sum of a subarray of size 3 in [4, 2, 1, 7, 8, 1, 2, 8, 1, 0] → Output: 17

It's commonly used in anagram detection, maximum subarray sum, and longest substring without repeating characters.


*1.3. Two Pointers*

Two indices scanning the array — from start and end or moving in sync. Great for reducing space/time complexity.

Example:

> Given [1, 2, 4, 4] and target = 8, return true if two numbers sum up to target → Output: True (4+4)

Common interview problems:

- Reverse a string/array

- Check for palindrome

- Remove duplicates in-place

- Merge two sorted arrays


*1.4. Prefix Sum*

Precompute cumulative sums to answer range queries in O(1) instead of O(n).

Example:

> For nums = [1, 2, 3, 4, 5], find sum from index 1 to 3 quickly → Output: 9 (2+3+4)



*Popular problems:*

- Subarray sum equals k
- Range sum queries
- Balanced subarrays


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Top 7 Coding Interview Concepts: https://whatsapp.com/channel/0029VammZijATRSlLxywEC3X/720