A practical coding interview preparation plan

A structured guide to deliberate practice

The goal of coding interview practice is not to memorize solutions. It is to recognize a useful approach, explain why it fits, implement it carefully, and test it under time pressure. A consistent review loop makes practice more valuable than simply increasing the number of problems you attempt.

Use the same loop for every practice problem

  1. Restate the problem. Explain the input, expected output, constraints, and what is unclear. Ask a clarifying question before committing to an interpretation.
  2. Work through a small example. Trace the example by hand. Add a second example that exposes a boundary case, such as an empty input, duplicate values, or a single item.
  3. Describe a straightforward approach. Establish a correct baseline first. Then identify its time and space costs and the bottleneck you want to improve.
  4. Choose a pattern and justify it. Consider whether the problem has a useful invariant or structure: a hash map for lookups, two pointers for ordered pairs, a sliding window for contiguous ranges, a stack for nested or monotonic relationships, or graph traversal for reachability.
  5. State the invariant before coding. Say what each important variable means and why it remains true as the algorithm runs. This makes implementation and debugging easier to follow.
  6. Test before you finish. Trace one normal case and relevant edge cases. Check loop bounds, duplicate handling, overflow assumptions, and whether the returned value matches the requested format.
  7. Summarize complexity. Explain the dominant time cost and any extra memory in terms of input size.

A four-week practice rhythm

Week 1 — Arrays, strings, and hash maps. Focus on frequency counting, prefix sums, two pointers, and sliding windows. Explain your brute-force baseline before optimizing.

Week 2 — Stacks, queues, linked lists, and binary search. Practice boundary conditions and be precise about loop invariants and pointer updates.

Week 3 — Trees, graphs, and recursion. Compare depth-first and breadth-first traversal; define visited-state and base cases explicitly.

Week 4 — Mixed timed sessions. Pick unseen problems across patterns, practice speaking while solving, and spend at least as much attention on review as on the timer.

Treat this as a starting template rather than a promise that four weeks is enough for every candidate. Adjust the time available and topic order to match the role, interview format, and your current strengths.

Keep a mistake log

After each session, record the problem type, the first approach you considered, where you got stuck, the key insight, and one action for next time. Label the cause of the miss: concept gap, missed constraint, unclear explanation, implementation bug, or rushed testing. Revisit problems you missed after a few days and solve them from a blank page.

Quick review template

Pattern: ____ · First idea: ____ · Bottleneck: ____ · Edge case missed: ____ · What I will say or do differently next time: ____

Practice communication, not just code

In a mock interview, narrate the decisions that matter: your interpretation, the options you considered, the invariant, and how you will verify the result. Pause to ask for feedback on clarity. If you use an AI tool while preparing, use it to generate a hint, challenge your reasoning, or review your explanation after an attempt; try the problem independently before looking at a full solution.

Explore the system design framework and behavioral answer guide for the other common interview formats.