23 — Algorithms

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▶️ pkg4algorithms/algorithms1SortingAlgorithms.java → algorithms7DivideAndConquer.java

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Package map

#	Topic	Algorithms	File
1	Sorting	Bubble, Selection, Insertion, Merge, Quick, Heap, Counting	algorithms1SortingAlgorithms
2	Searching	Linear, Binary, first/last occurrence	algorithms2SearchingAlgorithms
3	Greedy	Activity selection, interval scheduling	algorithms3GreedyAlgorithms
4	Dynamic Programming	Fibonacci, knapsack, LCS	algorithms4DynamicProgramming
5	Backtracking	Subsets, permutations, N-Queens	algorithms5Backtracking
6	Graph	Dijkstra, Topological sort, cycle detect	algorithms6GraphAlgorithms
7	Divide & Conquer	Merge sort, quickselect, binary search	algorithms7DivideAndConquer

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Big-O cheat sheet

Notation	Name	Example
O(1)	Constant	HashMap get
O(log n)	Logarithmic	Binary search
O(n)	Linear	Scan array
O(n log n)	Linearithmic	Merge sort
O(n²)	Quadratic	Nested loops
O(2ⁿ)	Exponential	Naive subsets

Always state time and space complexity in interviews.

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Pattern recognition

Problem signal	Try
Sorted array + find	Binary search
All subsets/permutations	Backtracking
Optimal substructure	Dynamic programming
Shortest path (non-negative)	Dijkstra
Dependencies / prerequisites	Topological sort
Top K elements	Heap
Subarray sum / window	Sliding window

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