The Archive of Interesting Code is an (ambitious) effort on my part to research, intuit, and code up every interesting algorithm and data structure ever invented. In doing so, I hope both to learn the mathematical techniques that power these technologies and to improve my skills as a programmer.

The examples on this site are in a variety of languages. I generally prefer to use C++ for algorithms, since the STL provides a great framework for expressing algorithms that work on a variety of data types. I code up most data structures in Java, both because the Collections framework allows them to be integrated in seamlessly with other applications and because automatic garbage collection simplifies some of the resource management. Every now and then I'll find an algorithm or data structure that is best represented in a different language like Haskell, in which case I'll forgo my usual language conventions.

In case you're curious what I'm someday hoping to having implemented on this page, you can check out my TODO list.

If you're interested in using any of this code in your applications, feel free to do so! You don't need to cite me or this website as a source, though I would appreciate it if you did. However, please don't plagiarize the code here by claiming authorship - that would just be dishonest. I also caution you that while I'm fairly confident that the code on this site is correct, I haven't mercilessly tested every line, and so there may be a lurking bug or two here.

Enjoy!

Name | Link | Date Added | Language | Description |
---|---|---|---|---|

Binomial Heap | (link) | 7‑24‑2010 | C++ | An implementation of a binomial heap data structure for use as a priority queue. |

Bounded Priority Queue | (link) | 7‑24‑2010 | C++ | An implementation of a priority queue with a fixed upper limit to its size.. |

Matrix | (link) | 7‑24‑2010 | C++ | A collection of classes for manipulating matrices. |

VList | (link) | 8‑16‑2010 | Java | An implementation of the List abstraction backed by a VList. |

Function Wrapper | (link) | 8‑16‑2010 | C++ | A C++ wrapper class around unary functions. |

String | (link) | 8‑17‑2010 | C++ | An implementation of a string abstraction that uses the small string optimization. |

nstream | (link) | 8‑31‑2010 | C++ | An stream class that sends and receives data over a network. |

Snake | (link) | 8‑31‑2010 | C++ | An implementation of the game Snake with a rudimentary AI. |

Mergesort | (link) | 9‑14‑2010 | C++ | An implementation of the mergesort algorithm. |

Next Permutation | (link) | 10‑6‑2010 | C++ | An implementation of the next_permutation STL algorithm. |

Interval Heap | (link) | 10‑17‑2010 | Java | An implementation of a double-ended priority queue using an interval heap. |

Linear-Time Selection | (link) | 10‑18‑2010 | C++ | A deterministic, linear-time selection algorithm using the median-of-medians algorithm. |

Heapsort | (link) | 10‑18‑2010 | C++ | An implementation of the heapsort algorithm. |

Union-Find | (link) | 10‑19‑2010 | Java | An implementation of a disjoint-set data structure using a disjoint set forest. |

Radix Sort | (link) | 10‑19‑2010 | C++ | An implementation of the radix sort algorithm. |

Rational | (link) | 10‑23‑2010 | C++ | A data structure representing a rational number. |

DPLL | (link) | 10‑23‑2010 | Haskell | An implementation of the DPLL algorithm for solving CNF-SAT. |

Smoothsort | (link) | 10‑27‑2010 | C++ | An implementation of the smoothsort algorithm, an adaptive heapsort variant. |

Extendible Array | (link) | 10‑28‑2010 | Java | A dynamic array class with O(1) worst-case runtime lookup and append. |

In-Place Merge | (link) | 10‑29‑2010 | C++ | An implementation of a merge algorithm that runs in-place. |

Random Shuffle | (link) | 10‑29‑2010 | C++ | An algorithm for generating a random permutation of a set of elements. |

Random Sample | (link) | 10‑29‑2010 | C++ | An O(n) time, O(1) space algorithm for randomly choosing k elements out of a stream with uniform probability. |

Natural Mergesort | (link) | 10‑30‑2010 | C++ | An implementation of natural mergesort, an adaptive variant of mergesort. |

Interpolation Search | (link) | 10‑31‑2010 | C++ | An implementation of the interpolation search algorithm. |

Introsort | (link) | 10‑31‑2010 | C++ | An implementation of the introsort algorithm, a fast hybrid of quicksort, heapsort, and insertion sort. |

Hashed Array Tree | (link) | 11‑3‑2010 | Java | An implementation of a dynamic array backed by a hashed array tree. |

Recurrence Solver | (link) | 11‑13‑2010 | C++ | A fast algorithm for generating terms of a sequence defined by a linear recurrence relation. |

Fibonacci Heap | (link) | 11‑15‑2010 | Java | An implementation of a priority queue backed by a Fibonacci heap. |

Dijkstra's Algorithm | (link) | 11‑16‑2010 | Java | An implementation of Dijkstra's algorithm for single-source shortest paths. |

Prim's Algorithm | (link) | 11‑17‑2010 | Java | An implementation of Prim's algorithm for computing minimum spanning trees. |

Kruskal's Algorithm | (link) | 11‑17‑2010 | Java | An implementation of Kruskal's algorithm for computing minimum spanning trees. |

Majority Element | (link) | 11‑17‑2010 | C++ | A fast, linear-time algorithm for finding the majority element of a data set. |

Haar Transform | (link) | 11‑17‑2010 | C++ | A set of functions to decompose a sequence of values into a sum of Haar wavelets. |

Argmax | (link) | 11‑19‑2010 | C++ | A pair of functions to compute the arg min or max of a function on some range. |

Derivative | (link) | 11‑19‑2010 | C++ | A function object that approximates the derivative of a function. |

Levenshtein Distance | (link) | 11‑19‑2010 | C++ | An algorithm for computing the Levenshtein distance between two sequences. |

Skiplist | (link) | 11‑20‑2010 | C++ | An implementation of a skip list, a randomized data structure for maintaining a sorted collection. |

van Emde Boas Tree | (link) | 11‑26‑2010 | C++ | An implementation of a sorted associative array backed by a van Emde Boas tree. |

Cuckoo HashMap | (link) | 11‑27‑2010 | Java | An implementation of a hash table using cuckoo hashing. |

Needleman-Wunsch Algorithm | (link) | 11‑28‑2010 | C++ | An implementation of the Needleman-Wunsch algorithm for optimal string alignment. |

Treap | (link) | 11‑28‑2010 | C++ | An implementation of a sorted associative array backed by a treap. |

Floyd-Warshall Algorithm | (link) | 12‑10‑2010 | Java | An implementation of the Floyd-Warshall algorithm for all-pairs shortest paths in a graph. |

Power Iteration | (link) | 12‑10‑2010 | C++ | An implementation of the power iteration algorithm for finding dominant eigenvectors. |

Edmonds's Matching Algorithm | (link) | 12‑15‑2010 | Java | An implementation of Edmonds's matching algorithm for finding maximum matchings in undirected graphs. |

Kosaraju's Algorithm | (link) | 12‑15‑2010 | Java | An implementation of Kosaraju's algorithm algorithm for finding strongly connected components of a directed graph. |

2-SAT | (link) | 12‑15‑2010 | Java | A linear-time algorithm for solving 2-SAT. |

Bellman-Ford Algorithm | (link) | 12‑17‑2010 | Java | An implementation of the Bellman-Ford algorithm for single-source shortest paths. |

Topological Sort | (link) | 12‑17‑2010 | Java | An algorithm for computing a topological sort of a directed acyclic graph. |

Graham Scan | (link) | 12‑19‑2010 | C++ | An implementation of the Graham scan for finding convex hulls in 2D space. |

Bipartite Testing | (link) | 12‑19‑2010 | Java | A linear-time algorithm for checking whether a directed graph is bipartite. |

Johnson's Algorithm | (link) | 12‑19‑2010 | Java | An implementation of Johnson's algorithm for all-pairs shortest paths. |

Strassen Algorithm | (link) | 12‑20‑2010 | C++ | An implementation of the Strassen algorithm for fast matrix multiplication. |

Cartesian Tree Sort | (link) | 12‑21‑2010 | C++ | An implementation of Cartesian tree sort, an adaptive, out-of-place heapsort variant. |

Ford-Fulkerson Algorithm | (link) | 12‑21‑2010 | Java | An implementation of the Ford-Fulkerson maximum-flow algorithm. |

Scaling Ford-Fulkerson | (link) | 12‑22‑2010 | Java | An modification of the Ford-Fulkerson maximum-flow algorithm that uses scaling to achieve polynomial time.. |

Splay Tree | (link) | 12‑27‑2010 | C++ | An implementation of a sorted associative array backed by a splay tree. |

Ternary Search Tree | (link) | 12‑28‑2010 | C++ | An implementation of a sorted set of strings backed by a ternary search tree. |

Ring Buffer | (link) | 12‑30‑2010 | Java | An implementation of a FIFO queue using a ring buffer. |

AVL Tree | (link) | 12‑30‑2010 | C++ | A sorted associative container backed by an AVL tree. |

Rabin-Karp Algorithm | (link) | 1‑1‑2011 | C++ | An implementation of the Rabin-Karp algorithm for string matching. |

RPN Evaluator | (link) | 1‑18‑2011 | C++ / strain | A library to tokenize and evaluate simple arithmetic expressions in reverse Polish notation. |

Shunting-Yard Algorithm | (link) | 1‑18‑2011 | C++ / strain | An implementation of Dijkstra's shunting-yard algorithm for converting infix expressions to reverse-Polish notation. |

Skew Binomial Heap | (link) | 1‑20‑2011 | C++ | An implementation of a priority queue backed by a skew binomial heap. |

2/3 Heap | (link) | 3‑1‑2011 | C++ | An implementation of a priority queue whose branching factor alternates at different levels to maximize performance. |

Zeckendorf Logarithm | (link) | 3‑10‑2011 | C++ | An algorithm based on Zeckendorf representations that efficiently computes logarithms. |

Factoradic Permutations | (link) | 3‑17‑2011 | C++ | A set of algorithms for generating permutations using the factoradic number system. |

Binary Cyclic Subsets | (link) | 3‑20‑2011 | C++ | A set of algorithms for generating subsets in lexicographical order using binary numbers and cyclic shifts. |

Fibonacci Iterator | (link) | 3‑22‑2011 | C++ | An STL-style iterator for iterating over the Fibonacci numbers. |

Fibonacci Search | (link) | 3‑22‑2011 | C++ | An implementation of the Fibonacci search algorithm. |

Euclid's Algorithm | (link) | 4‑18‑2011 | Haskell | An implementation of Euclid's algorithm and applications to continued fractions and the extended Euclidean algorithm. |

Find Duplicate | (link) | 4‑18‑2011 | Python | An algorithm to find a repeated element in an array using Floyd's cycle-finding algorithm. |

Permutation Generator | (link) | 4‑19‑2011 | Python | A generator for producing all permutations of a list of elements. |

Matrix Find | (link) | 4‑19‑2011 | Python | A solution to the classic interview question of searching a sorted matrix for a particular value. |

Binary GCD | (link) | 4‑23‑2011 | Scheme | An implementation of the binary GCD algorithm for computing greatest common divisors of nonnegative integers. |

Knuth-Morris-Pratt Algorithm | (link) | 5‑3‑2011 | Python | An implementation of the Knuth-Morris-Pratt algorithm for fast string matching. |

Kadane's Algorithm | (link) | 5‑7‑2011 | C++ | An implementation of Kadane's algorithm for solving the maximum-weight subarray problem. |

Karatsuba's Algorithm | (link) | 8‑15‑2011 | Python | An implementation of Karatsuba's algorithm for fast integer multiplication. |

Min-Stack | (link) | 8‑15‑2011 | C++ | An implementation of a LIFO stack that supports O(1) push, pop, and find-minimum. |

Random Bag | (link) | 8‑15‑2011 | Python | A data structure that supports insertion and removal of a uniformly-random element. |

Min-Queue | (link) | 8‑15‑2011 | C++ | An implementation of a FIFO queue that supports O(1) push, pop, and find-minimum. |

Lights-Out Solver | (link) | 8‑29‑2011 | C++ | A solver for the game Lights Out using Gaussian elimination over GF(2). |

Maximum Single-Sell Profit | (link) | 11‑9‑2011 | Python | Four algorithms for the maximum single-sell profit problem, each showing off a different algorithmic technique. |

Generalized Kadane's Algorithm | (link) | 11‑10‑2011 | C++ | A generalization of Kadane's algorithm for solving the maximum subarray problem subject to a length restriction. |

Longest Range | (link) | 11‑19‑2011 | Java | An algorithm for solving the longest contiguous range problem. |

Egyptian Fractions | (link) | 11‑20‑2011 | Python | An implementation of the greedy algorithm for finding Egyptian fractions. |

LL(1) Parser Generator | (link) | 11‑21‑2011 | Java | An LL(1) parser generator. |

LR(0) Parser Generator | (link) | 11‑23‑2011 | Java | An LR(0) parser generator. |

Word Ladders | (link) | 11‑27‑2011 | JavaScript | A program for finding word ladders between two words. |

Alias Method | (link) | 12‑27‑2011 | Java | An implementation of the alias method for sampling from a discrete probability distribution. |

Binary Quicksort | (link) | 1‑5‑2012 | C++ | An implementation of the binary quicksort (binary MSD radix sort) algorithm. |

Ternary Sierpinski Triangle | (link) | 6‑16‑2012 | JavaScript | An algorithm for drawing the Sierpinksi triangle using ternary numbers. |

In-Place Tree Delete | (link) | 12‑12‑2012 | C++ | An algorithm for deleting all of the nodes of a binary tree using O(1) auxiliary storage space. |

Random Access List | (link) | 5‑14‑2013 | Haskell | A purely functional, persistent random-access sequence backed by a random access list. |

BST LCA | (link) | 6‑5‑2013 | Haskell | A function for finding the lowest common ancestor of two nodes in a binary search tree. |

Matrix Fill | (link) | 3‑6‑2014 | Java | An algorithm for solving the matrix fill problem, an interview problem from Microsoft. |