Data Structure and Algorithm Selection Guide

Data Structure Selection

Need	First Choice	Alternative	Avoid
Fast lookups by key	Hash Map (`Dictionary<K,V>`)	Sorted array + binary search	Linear search in array
Fast insertion/removal at ends	Dynamic Array (`List<T>`)	Deque	Linked list (unless memory critical)
Maintain sorted order during insertions	Balanced BST or `SortedDictionary<K,V>`	Sorted list + binary insertion	Unbalanced BST
Priority-based processing	Heap (`PriorityQueue<T,P>`)	Sorted list	Unsorted array
Function call management	Stack	Array with index	Queue
Task queue/scheduling	Queue	Array with indices	Stack
Undo/Redo operations	Stack of states	Array	Queue
Cache with size limit	LRU Cache (dict + doubly linked)	Hash map only	Array

Problem Type	First Try	If That Fails	Never Use
Sorting small data (<50 items)	Language built-in	Insertion sort	Bubble sort
Sorting large data	Language built-in	Merge sort	Selection sort
Searching unsorted	Linear search (built-in)	Hash set conversion	Binary search
Searching sorted	Binary search	Built-in search	Linear search
Shortest path (unweighted)	BFS	Library pathfinding	DFS
Shortest path (weighted)	Dijkstra’s	A* with heuristic	BFS on weighted
Finding any path	DFS	BFS	Complex pathfinding
Tree traversal	Built-in iterator	Recursive DFS/BFS	Manual stack