A pattern-first interview workbook
Reasoning Into Code
250 deliberate katas for coding interviews.
Understanding an algorithm and writing it correctly are different skills. This book builds the bridge: define the state, name the invariant, write the protocol, trace the transitions, then turn the reasoning into executable Python.
Arunank Divya Sharan · First edition · September 2026
- complete lessons
- 250
- ordered modules
- 25
- PDF pages
- 955
Inside every lesson
A precise question
An explicit contract, constraints and concrete input/output examples.
A reasoning protocol
State, invariants, safe updates and the bridge from pseudocode to code.
A visible execution
Diagrams and worked traces that show how the state changes.
A complete reference
Python implementation, correctness argument, complexity, pitfalls and a reasoning card.
One deliberate progression
The original problem order is preserved. Later lessons build on the habits established earlier.
Learn to express state
Scans, hashing, sorting, two pointers, sliding windows and prefix state.
Control the frontier
Stacks, queues, heaps, intervals, linked lists and binary search.
Traverse and decompose
Matrices, grids, recursion, backtracking, trees and tries.
Connect the patterns
Graphs, union-find, greedy choices, dynamic programming, bits and designed structures.
Start with one problem
Read the question first. Try the solution before opening the explanation, then compare your state and transitions with the trace.