Data Structures

List of pages of notes on the wiki related to data structures:

Elementary Data Structures

An important topic that connects each of the concepts below is the Abstract Data Type, which is a general implementation/interface intended to be common to these data containers across both Java and Python

Arrays

• array-based data structures, storage, and algorithms
• lower-level structure that can be implemented by many higher-level data structures
• Python has a built-in array-based list() type, everything (including integers) is reference-based - Arrays/Python
• Java has Array type, size must be known at creation time - Arrays/Java
• Can implement a Python list type in Java - see Arrays/Java/PythonList
• Many data structures below can be implemented under the hood as array-based or linked structure based

StacksQueues

• Stacks, queues, and deques are important structures for O(1) access to front/back, order in determines order out

Lists

• Lists have two main implementations - array-based lists (in Python, this is a natural place to start, due to Python's built-in list type) or object- and link-based (in Java, this is more natural due to the way the language principally focuses on objects).
• Linked Lists can be implemented in either Python or Java - see Linked Lists/Python or Linked Lists/Java
• ArrayLists are a type in Java but are also similar to the array-based list data structure built into Python

Trees

• Tree structures are nonlinear data structures that extend the idea of a linked list node and data pointer organization.
• A tree is a directed acyclic graph consisting of parent nodes and child nodes, such that all nodes have one parent (except the top-level root node). Typically number of children n is fixed.
• Nodes without children are leaf nodes/external nodes. Nodes with one or more children are internal nodes.
• Binary Trees are a tree structure where each node has a maximum of two children:
  • Each node has a maximum of two children
  • Each child node is labeled as left or right
• Left precedes right in order of children of a node
  • Proper/full - each node has 0 or 2 children
  • Improper - one or more nodes have 1 child
• Recursive binary tree definition:
  • A node r, called root of T, stores an element
  • A binary tree, possibly empty, called left subtree of T
  • A binary tree, possibly empty, called right subtree of T
• Binary Trees/Python
• Binary Search Trees

Dictionaries