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Post-order traversal in a tree
In this traversal method, the root node is visited last, hence the name. First we traverse the left subtree, then the right subtree and finally the root node.
![Post-order Traversal Tree](/java_data_structures/images/postorder_traversal_tree.jpg)
We start from A, and following Post-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
Algorithm
Until all nodes are traversed −
Step 1 − Recursively traverse left subtree. Step 2 − Recursively traverse right subtree. Step 3 − Visit root node.
Example
class Node{ int data; Node leftNode, rightNode; Node() { leftNode = null; rightNode = null; this.data = data; } Node(int data) { leftNode = null; rightNode = null; this.data = data; } int getData() { return this.data; } Node getleftNode() { return this.leftNode; } Node getRightNode() { return this.leftNode; } void setData(int data) { this.data = data; } void setleftNode(Node leftNode) { this.leftNode = leftNode; } void setRightNode(Node rightNode) { this.leftNode = rightNode; } } public class PostOrderBinaryTree { public static void main(String[] args) { Node node = new Node(50); node.leftNode = new Node(60); node.leftNode.leftNode = new Node(45); node.leftNode.rightNode = new Node(64); node.rightNode = new Node(60); node.rightNode.leftNode = new Node(45); node.rightNode.rightNode = new Node(64); System.out.println("post-order arrangement of given elements: "); postOrder(node); } public static void postOrder(Node root) { if(root !=null) { postOrder(root.leftNode); postOrder(root.rightNode); System.out.println(root.data); } } }
Output
post-order arrangement of given elements: 45 64 60 45 64 60 50
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