Algorithms & Data Structures

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Algorithms & Data Structures

Back-end interviews often test your ability to pick the right data structure for the job.

Foundational Structures

Array / List - : fast index access, slow insertions in the middle.
Hash Map / Object - : O(1) average lookup, ideal for counting and memoization.
Stack / Queue - : useful for parsing, BFS, and DFS.
Tree - : hierarchical data; binary search trees enable ordered lookup.
Graph - : relationships and networks; BFS and DFS traverse them.

Common Patterns

  • Two pointers for sorted arrays.
  • Sliding window for subarrays.
  • Hash maps for frequency and duplicate detection.
  • Recursion + memoization for tree and graph problems.

Knowing when to use each structure is more important than memorizing every algorithm.

Comprehension check

Answer all 3 questions correctly to unlock Submit.

1Which data structure provides O(1) average lookup time?

2Which pattern is best for finding the sum of every contiguous subarray of size k?

3When is a stack a good choice?