Postorder Tree Traversal in Binary Tree in C

A binary tree is a hierarchical data structure in computer science. Each node in a binary tree can have at most two children: a left child and a right child. There are several ways to traverse a binary tree and in this article, we will learn about the postorder traversal of a binary tree in C.

Example

Input:   
     1        
   /   \       
  2    3      
 / \  / \    
4  5 6  7

Output:
Postorder Traversal : 4 5 2 6 7 3 1

Postorder Tree Traversal in Binary Tree in C

The postorder traversal is a way of visiting all the nodes of a binary tree in a specific order. It involves visiting the left subtree first, followed by the right subtree, and finally the root node. Consider the below diagram to understand the workflow of postorder traversal:

Workflow of Postorder Traversal

Algorithm for Postorder Traversal in C

Following is the algorithm for the postorder traversal of the binary tree in C:

1. Start
2. Traverse left subtree using recursion.
3. Traverse right subtree using recursion
4. Visit the root node
5. Repeat steps 3-5 until root node != NULL
6. Stop

C Program for Postorder Traversal in a Binary Tree

The following program demonstrates how we can implement the postorder traversal in a binary tree in C:

// C Program for Postorder Traversal in a Binary Tree
#include <stdio.h>
#include <stdlib.h>

// __________ CODE FOR BINARY TREE IMPLEMENTATION __________

// Define the structure for a binary tree node
struct Node {
    int data;
    struct Node* left;
    struct Node* right;
};

// Function to create a new node in a Binary Tree
struct Node* createNode(int data)
{
    // Allocate memory for the new node
    struct Node* newNode
        = (struct Node*)malloc(sizeof(struct Node));
    // Initialize node data and children pointers
    newNode->data = data;
    newNode->left = NULL;
    newNode->right = NULL;
    return newNode;
}

// __________ CODE FOR POSTORDER TRAVERSAL  __________

// Function to perform postorder traversal
void postorderTraversal(struct Node* root)
{
    if (root != NULL) {
        postorderTraversal(root->left);
        postorderTraversal(root->right);
        printf("%d ", root->data);
    }
}

// driver code
int main()
{
    struct Node* root = NULL;

    // Create the binary tree
    /*     1
                 /   \
             2    3
                / \  / \
                4  5 6  7
    */
    root = createNode(1);
    root->left = createNode(2);
    root->right = createNode(3);
    root->left->left = createNode(4);
    root->left->right = createNode(5);
    root->right->left = createNode(6);
    root->right->right = createNode(7);

    // Perform postorder traversal
    printf("Postorder traversal of the binary tree is:\n");
    postorderTraversal(root);
    printf("\n");

    return 0;
}

Postorder traversal of the binary tree is:
4 5 2 6 7 3 1 

Time Complexity: O(N), where N denotes the number of nodes in the binary tree
Auxiliary Space: O(log N),if space of recursive stack is not considered. If the tree is skew, then O(N)

Applications of Postorder Traversal

Following are some use cases for the post-order traversal of a binary tree:

• Used to evaluate postfix expression.
• Used to convert mathematical expressions like infix to postfix conversion.
• Used to delete or free the memory occupied by a binary tree.
• Used in compiler design for code generation and optimization tasks.
• Used in the construction and traversal of threaded binary trees.

Related Articles

The following are some articles about the post order traveral of a binary tree that can improve your knowledge:

• Types of Tree traversals
• Postorder of Binary Tree without recursion and without stack
• Find Postorder traversal of BST from preorder traversal
• Iterative Postorder traversal (using two stacks)
• Iterative Postorder traversal (using one stack)

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Article Tags :

• C Language
• C Examples
• C-DSA
• misc-c