Preorder Tree Traversal of Binary Tree in C

February 28, 2023

Direction (Inorder)	Anti- Clockwise
Rule	Center Left Right (CLR)

Understanding Preorder Traversal in Binary Tree in C

On this page we will discuss about Preorder Tree Traversal of Binary Tree in C . Preorder Tree traversal is where we try print the center most node first, i.e. the root node first and then we go ahead and print the left and then right node. The order of printing thus in anti-clockwise format.

Preorder Tree Traversal in Binary Tree in C Language

Implementing PreOrder Traversal

The direction of traversal for preorder is anti-clockwise
Rule followed is CLR (Center-Left-Right)

What we mean by above is that we try to visit the central node i.e. the root node first and once, there are no central node, we move to left node and right thus forming an anti-clockwise direction.

Check the example below –

Explanation for PreOrder Traversal in Binary Tree

Start Traversing
Central Node (1): Print, Traverse left
Central Node (2): Print, Traverse left
Central Node (4) : Print Traverse Left
Left Node : Print Traverse Right
Recur up to Subtree of 2 Print Right node 5
The whole left subtree of Root node has been printed now go to right subtree of root node
Central Node (2) : Print, traverse Left
Central Node (6), print traverse left
No more left node traverse right print 10
Traverse right for 7 central node print, recur left
Print 11 (left node)
Print 12 (right node)

Priority Queue in C

Tree Traversals: Inorder Postorder Preorder

Inorder Tree Traversal in Binary Tree

Postorder Tree Traversal in Binary Tree

Preorder Tree Traversal without Recursion

Run

// Program for tree traversal preorder in Binary Tree
#include<stdio.h>
#include<stdlib.h>
// We are creating struct for the binary tree below
struct node
{
  int data;
  struct node *left, *right;
};

// newNode function for initialisation of the newly created node
struct node *newNode (int item)
{
  struct node *temporary = (struct node *) malloc (sizeof (struct node));
  temporary->data = item;
  temporary->left = temporary->right = NULL;
  return temporary;
}

// Here we print the preorder recursively
void preorder (struct node *root)
{
  if (root != NULL)
    {
      printf ("%d ", root->data);
      preorder (root->left);
      preorder (root->right);
    }
}

// Basic Program to insert new node at the correct position in BST
struct node *insert (struct node *node, int data)
{
  /* When there no node in the tree(subtree) then create 
   and return new node using newNode function */
  if (node == NULL)
    return newNode (data);

  /* If not then we recur down the tree to find correct position for insertion */
  if (data < node->data)
    node->left = insert (node->left, data);
  else if (data > node->data)
    node->right = insert (node->right, data);

  return node;
}

int main ()
{
  /* What our binary search tree looks like really 
      9 
     / \ 
    7  14
   / \ / \ 
  5  8 11 16 */
  
  struct node *root = NULL;
  root = insert (root, 9);
  insert (root, 7);
  insert (root, 5);
  insert (root, 8);
  insert (root, 14);
  insert (root, 11);
  insert (root, 16);

  printf ("The preorder is :\n");
  preorder (root);

  return 0;
}

Output:

The preorder is :
9 7 5 8 14 11 16

In the above example first root node i.e. 1 get traversed then, using the CLR rule it will traverse the left node i.e. 25 get traversed, then again CLR rule get applied and 7 will get traversed now no left node is left here so it will traverse right node i.e. 15 here , then 14 , then using CLR remaining 22 and 28 will get traversed. The image below will help you to understand in a better way.

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