Algorithms and data structures collected over time.

Python Examples

• Two Pointer
• Sliding Window
• Queues
• Stacks
• Linked List
• Trees
• Binary Search Tree (BST)
• Heaps
• Backtracking, Subsets, Permutations
• Graphs

Algorithms

• MST of a Graph - Prims Algorithm
• Shortest Path - Dijkstra's
• Manhattan Distance
• Boyer Moore Pattern Searching

Concepts / Data Structures / Patterns

• Big O
• Arrays & Strings
• Hashmaps & Hashsets
• Two Pointers
• Binary Search
• Linked Search
• Stacks & Queues
• Sliding Window
• Recursion
• Trees
• Heaps / Priority Queues
• Backtracking
• Graphs
• Dynamic Programming

Cheat sheet

Common numbers

• 26 - alphabet
• 52 - alphabet capitalized

Java APIs

• String
• Character
• ArrayList
• Collections
• HashMap
• HashSet
• PriorityQueue
• Deque
• Iterator
• TreeMap

Task	API	Example	Notes
Sort an array (ascending)	Arrays.sort(...)	int[] a = {3,1,2}; Arrays.sort(a);	Primitives sort ascending. For objects, you can pass a Comparator.
Binary search in a sorted array	Arrays.binarySearch(...)	int i = Arrays.binarySearch(a, target);	Array must be sorted. Returns index if found, otherwise -(insertionPoint) - 1.
Sort a string (lexicographic)	toCharArray(), Arrays.sort(...), new String(...)	char[] c = s.toCharArray(); Arrays.sort(c); String t = new String(c);	Sorts by Unicode code point. Use s.toLowerCase() first if you want case-insensitive behavior.
Integer min/max value	Integer.MIN_VALUE, Integer.MAX_VALUE	int lo = Integer.MIN_VALUE, hi = Integer.MAX_VALUE;	Useful as sentinels and bounds in algorithms.
Double infinity	Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY	double inf = Double.POSITIVE_INFINITY;	Also: Double.isInfinite(x) to check.