### Summary

Tree Traversal is a way to visit or examine all the nodes in a tree data structure. The goal is to analyze the values stored in every node, monitor their pattern, and make decisions based on this data.

### ELI5

Imagine you want to visit all your friends who live in different treehouses in a large tree. You have your own way of visiting each house one by one. Maybe you start from the bottom and work your way to the top, or you visit them in a certain order. This is exactly what tree traversal does; it’s about visiting each ’treehouse’ (or node in the tree) in a particular order.

### In-depth explanation

In computer science, Tree Traversal (also known as tree search) refers to the process of visiting (checking and/or updating) each node in a tree data structure, exactly once. The traverse operation is a fundamental procedure employed to manipulate or access the information of each node within the tree.

Tree traversal can be done in multiple ways, and the three most common approaches are In-Order, Pre-Order, and Post-Order traversal – referring to the order in which each node’s value or key is accessed with respect to the values/keys of its adjacent nodes. While Pre-Order traversal accesses the current node before its child nodes, In-Order traversal accesses the current node between visiting its child nodes and Post-Order traversal checks the current node after visiting both its left and right child.

One could easily imagine implementing a recursive function to perform tree traversals. For example, the Python code for a pre-order traversal might look like this:

def preorder_traversal(node): if node is not None: print(node.value) preorder_traversal(node.left) preorder_traversal(node.right)

In this snippet, each node is processed (in this case, printed) before its child nodes. Precise definitions for In-Order and Post-Order traversal are similar but involve swapping the order of operations.

Tree Traversal is fundamental in many aspects of artificial intelligence (AI) and machine learning (ML), primarily in algorithmic decision-making processes. For example, decision trees, a commonly used machine learning technique, heavily depend on tree traversal methods to make decisions or classify entities.

### Related Terms

Decision Trees, Depth-First Search (DFS), Breadth-First Search (BFS), Graph Traversal, Binary Trees, Data Structures, Recursion.