Quick Reference

Fast access to essential algorithms and problem-solving strategies.

Contents

Resource	Description
Study Guide	Learning path, pattern recognition, interview patterns
Code Templates	Ready-to-use algorithm implementations
Advanced Algorithms	FFT, HLD, Persistent Segment Tree, etc.
Common Mistakes	Pitfalls to avoid

Quick Decision Guide

I see…	I think…	I use…
Sorted array	Binary search	bisect_left/right
Subarray sum	Prefix sum	prefix[r] - prefix[l]
Next greater	Monotonic stack	while stack and ...
Shortest path	BFS (unweighted)	deque + visited
Min/max path	Dijkstra	heapq + distance
Connected?	Union-Find	find + union
Count ways	DP	dp[i] = ...

Constraint-Based Selection

Constraint	Max Complexity	Examples
n <= 10	O(n!)	Brute force
n <= 20	O(2^n)	Bitmask DP
n <= 500	O(n^3)	Floyd-Warshall
n <= 5000	O(n^2)	Simple DP
n <= 10^5	O(n log n)	Sorting, Segment Tree
n <= 10^6	O(n)	Linear scan