Module 3 · Recursion, trees and the questions you cannot prepare for Lesson 11 of 15
A 4-week practice plan, condensed
Four weeks is enough for patterns, not for hundreds of problems. Two problems a day, narrated out loud, beats twenty problems read.
The concept
Four weeks, one topic a week, two problems a day of which one is new and one is a repeat from three days ago. Week 1 arrays, strings and hashing. Week 2 two pointers, sliding window and sorting. Week 3 recursion, trees and BFS. Week 4 revision of everything you got wrong, typed again from scratch.
Keep a file per problem with three lines: the pattern, the complexity, and the specific mistake you made. That file is what you revise from, not the solutions — reading a solution you have already understood teaches almost nothing. Before an interview, read only your mistake file.
Wk1 arrays, strings, hashing
Wk2 two pointers, sliding window, sorting
Wk3 recursion, trees, BFS
Wk4 redo everything you got wrong, typed from scratch
2 problems a day: 1 new + 1 repeat from three days ago.
Keep a file: the pattern . the complexity . the mistake you made.Common mistakes
The mistake is grinding new problems for hours a day and never repeating. Fluency comes from the second and third attempt at the same problem a few days apart, and that is exactly what most candidates skip because a new problem feels more productive.
Worked example
A day of ten problems read and not solved is worth less than two solved on paper with the complexity written underneath.
Your practice task
Book 28 daily slots in your calendar, two problems each, and mark each one solved-on-paper-yes-or-no.
Do this before moving on. Reading a solution teaches the shape of it; typing it teaches you.
Key takeaway
Four weeks, one topic a week, two problems a day of which one is new and one is a repeat from three days ago.
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