A 30-Day Coding Interview Study Plan That Actually Works

Preparing for coding interviews can feel endless because there are thousands of problems. The good news is that interviews reuse a small set of patterns. This plan assumes one to two hours a day and focuses on understanding rather than volume.

Before you start

• Pick one language and stay with it. Python, Java and C++ are all fine.
• Create a simple notebook or document for mistakes and patterns.
• Set a timer. Interviews are timed, so practise like it.

Week 1: arrays, strings and hash maps

Solve 8 to 10 easy and medium problems. Learn to count with dictionaries, to use sets for fast lookups, and to recognise when sorting simplifies a problem. Good starters: Two Sum, Valid Anagram, Group Anagrams, Contains Duplicate.

Week 2: two pointers, sliding window and binary search

These three patterns solve a large share of medium problems. For each one, solve a fixed example, then a variation. If you cannot solve a problem in 25 minutes, read the hint, then re-solve it from scratch the next day.

Week 3: linked lists, trees and graphs

Draw pictures. For trees, practise both recursive DFS and iterative BFS. For graphs, learn adjacency lists, visited sets and grid traversal. Revisit Week 1 and 2 problems you found hard.

Week 4: dynamic programming and mock interviews

Spend the first half of the week on DP basics (stairs, coin change, house robber). Spend the second half on mock interviews with a friend or by explaining your solution out loud while you code.

Daily routine

1. 10 minutes: review yesterday’s notes.
2. 45 to 60 minutes: one or two new problems.
3. 10 minutes: write down what pattern the problem used and what you got wrong.

How to communicate in the interview

State the problem in your own words, give a brute-force idea first, then improve it. Mention time and space complexity, test with a small example and discuss edge cases such as empty input and duplicates. Interviewers value clear thinking as much as the final code.

Common mistakes

• Reading solutions too early. Struggle for a while first; it is where learning happens.
• Doing many problems once instead of fewer problems twice.
• Skipping explanations. If you cannot explain it, you do not own it yet.

Adjust the plan to your schedule, and remember that consistency beats long, irregular sessions.