🐍 Python Coding Interview Reference

Two companion documents for coding interview prep:

File	Purpose	When to read
CHEATSHEET.md	Pure Python syntax and idioms	The 30 seconds before a round — "what does bisect_left return again?"
PATTERNS.md	Algorithm templates and techniques	The night before — "how does the monotonic-stack template go?"

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What's in CHEATSHEET.md

Syntax-only, one-liners, no algorithms.

• Basic types: integers (incl. base conversion), strings, booleans
• Built-in data structures: lists, sets, dicts, tuples, stacks, deques
• Node skeletons for linked lists and trees
• collections: Counter, defaultdict, OrderedDict, deque
• heapq, math, string, random, itertools, bisect, functools
• sortedcontainers (SortedList / SortedDict / SortedSet)
• Comprehensions, generators, lambdas
• Scope (global / nonlocal)
• Classes (essentials only — __init__, __str__, __eq__, __lt__, @property, inheritance)
• Common idioms (enumerate, zip, unpacking, transpose, etc.)
• Performance tips and Big-O reference

What's in PATTERNS.md

Algorithm templates — full implementations you can adapt.

• Searching: Binary Search (both patterns), Binary Search on Answer
• Two-pointer family: Two Pointers, Fast & Slow Pointers, Sliding Window
• Array tricks: Prefix Sum (1D & 2D), Monotonic Stack, Intervals
• Top-K: Heap (top-K, k-closest, merge-K, median of stream), Quickselect
• Strategies: Greedy, Backtracking, Dynamic Programming
• Bits & math: Bit Manipulation, Math / Number Theory (sieve, modpow)
• Data structures: Linked Lists, Trees, BSTs, Matrix, Graphs (incl. multi-source BFS, 0-1 BFS), Trie, Union-Find
• Design: LRU Cache (OrderedDict + from-scratch DLL versions)

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Interview-Day Tips

1. Clarify the problem. Input/output format, edge cases, assumptions.
2. Brute force first, then optimize. A correct slow solution beats a broken fast one.
3. Think out loud. Walk through your approach and examples before coding.
4. Test your code. Walk through with examples; check off-by-one errors and empty inputs.
5. State complexity. Always analyze and discuss time/space trade-offs.

Patterns to drill

Two pointers · Sliding window · Binary search · DFS/BFS · Dynamic programming · Backtracking · Monotonic stack · Heap / top-K · Prefix sum · Intervals · Union-Find

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Happy coding! 🚀