What is Tree Traversals (Inorder, Preorder and Post order)?

Introduction

Traversal is a process to visit all the nodes of a tree and may print their values too. Because, all nodes are connected via edges (links) we always start from the root (head) node. That is, we cannot randomly access a node in a tree. There are three ways which we use to traverse a tree.

• In-order Traversals
• Pre-order Traversals
• Post-order Traversals 

Inorder Traversal

In this traversal method, the left sub tree is visited first, then the root and later the right sub-tree. We should always remember that every node may represent a sub tree itself.

If a binary tree is traversed in-order, the output will produce sorted key values in an ascending order.

>  We start from A, and following in-order traversal, we move to its left sub tree B. B is also traversed in-order. The process goes on until all the nodes are visited. The output of inorder traversal of this tree will be −

>  D → B → E → A → F → C → G

Preorder Traversal

In this traversal method, the root node is visited first, then the left sub tree and finally the right sub tree.

 

>  We start from A, and following pre-order traversal, we first visit A itself and then move to its left sub tree B. B is also traversed pre-order. The process goes on until all the nodes are visited. The output of pre-order traversal of this tree will be −

>  A → B → D → E → C → F → G

Postorder Traversal

In this traversal method, the root node is visited last, hence the name. First we traverse the left sub tree, then the right sub tree and finally the root node.

 

>  We start from A, and following pre-order traversal, we first visit the left subtree B. B is also traversed post-order. The process goes on until all the nodes are visited. The output of post-order traversal of this tree will be −

>  D → E → B → F → G → C → A