Tag: tree data structure

About

In computer science, a tree is a widely-used data structure that emulates a tree structure with a set of linked nodes.

Nodes

A node may contain a value or a condition or represents a separate data structure or a tree of its own. Each node in a tree has zero or more child nodes, which are below it in the tree (by convention, trees grow down, not up as they do in nature). A node that has a child is called the child's parent node (or ancestor node, or superior). A node has at most one parent. The height of a node is the length of the longest downward path to a leaf from that node. The height of the root is the height of the tree. The depth of a node is the length of the path to its root (i.e., its root path).

Root nodes

The topmost node in a tree is called the root node. Being the topmost node, the root node will not have parents. It is the node at which operations on the tree commonly begin (although some algorithms begin with the leaf nodes and work up ending at the root). All other nodes can be reached from it by following edges or links. (In the formal definition, each such path is also unique). In diagrams, it is typically drawn at the top. In some trees, such as heaps, the root node has special properties. Every node in a tree can be seen as the root node of the subtree rooted at that node.

Leaf nodes

Nodes at the bottommost level of the tree are called leaf nodes. Since they are at the bottommost level, they do not have any children.

Internal nodes

An internal node or inner node is any node of a tree that has child nodes and is thus not a leaf node.

Subtrees

A subtree is a portion of a tree data structure that can be viewed as a complete tree in itself. Any node in a tree T, together with all the nodes below it, comprise a subtree of T. The subtree corresponding to the root node is the entire tree; the subtree corresponding to any other node is called a proper subtree (in analogy to the term proper subset).

From en.wikipedia.org/wiki/Tree_data_structure

Working with trees When working with tree data structures you often need to craft them in different ways. PHP offers a lot of functions to change the shape of arrays, but often they only go 1 level deep. Trees can count an almost infinite number of levels. Hence we need recursive replacements for our beloved array & string functions.