Preorder Traversal Without Recursion in C++

March 3, 2023

Preorder Traversal Without Recursion

There are three types of traversals in trees: Preorder,Inorder,Postorder. The traversals can be performed using recursion or stack. In this article, preorder traversal is performed using stack.

Preorder tree traversal in binary tree without recursion in cpp

More About Preorder Traversal

  1. Preorder traversal is a depth first algorithm.
  2. We first print the value of the node,them move to the left subtree and finally to the right subtree.
  3. If we need to explore more about the node itself before inspecting its leaves, we use preorder traversal.
  4. Preorder traversal is used to find the prefix expression of an expression tree.
Preorder Tree Traversal in binary tree in C++

Algorithm:

  1. If root is empty, return.
  2. Push root to stack.
  3. Continue until stack is not empty.
  4. Print the top element of stack.
  5. Add the right and the left child of the top element.
Example -Preorder Traversal
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Inorder Postorder Preorder Traversal Examples

Preorder Tree Traversal in Binary Tree

Postorder Tree Traversal in Binary Tree

Inorder Tree Traversal without Recursion

Postorder Tree Traversal without Recursion

Code Implementation for Preorder Tree traversal without recursion

Run 
#include<bits/stdc++.h>
using namespace std;
class Tree
{
public:
  int data;
  Tree *left = NULL, *right = NULL;
  // Constructor initialised
    Tree (int x)
  {
    data = x;
    left = NULL;
    right = NULL;
  }
};
void preorder (Tree * root)
{
  // If empty return;
  if (root == NULL)
    return;
  stack < Tree * >s;
  s.push (root);
  // Continue till stack is empty 
  while (!s.empty ())
    {
      Tree *temp = s.top ();
      // Print data
      cout << temp->data << " ";
      // Remove Data
      s.pop ();
      // Add right child
      if (temp->right != NULL)
	s.push (temp->right);
      // Add Left child
      if (temp->left != NULL)
	s.push (temp->left);
    }
}

int main ()
{
  Tree *root = new Tree (10);
  root->left = new Tree (20);
  root->right = new Tree (30);
  root->left->left = new Tree (40);
  root->left->right = new Tree (50);
  cout << "Preorder Traversal" << endl;
  preorder (root);
  return 0;
}



Output:

Preorder Traversal
10 20 40 50 30

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Introduction to Trees

Binary Trees

Binary Search Trees

Traversals

  • Traversal in Trees
  • Tree Traversals: Breadth-First Search (BFS) : C | C++ | Java
  • Tree Traversals: Depth First Search (DFS) : C | C++ | Java
  • Construct a Binary Tree from Postorder and Inorder

B – Trees

AVL Trees

  • AVL Trees
    • AVL Trees: Introduction
    • AVL Tree Insertion : C | C++ | Java
    • AVL Tree Deletion : C | C++ | Java
    • Insertion in a Binary Tree (Level Order) – C | C++ | Java
    • Searching in Binary Tree – C | C++ | Java
    • Searching in a Binary Search Tree – C | C++ | Java

Complete Programs for Trees

  • Depth First Traversals – C | C++ | Java
  • Level Order Traversal – C | C++ | Java
  • Construct Tree from given Inorder and Preorder traversals – C | C++ | Java
  • Construct Tree from given Postorder and Inorder traversals – C | C++ | Java
  • Construct Tree from given Postorder and Preorder traversal – C | C++ | Java
  • Find size of the Binary tree – C | C++ | Java
  • Find the height of binary tree – C | C++ | Java
  • Find maximum in binary tree – C | C++ | Java
  • Check whether two tree are identical- C| C++| Java
  • Spiral Order traversal of Tree- C | C++| Java
  • Level Order Traversal Line by Line – C | C++| Java
  • Hand shaking lemma and some Impotant Tree Properties.
  • Check If binary tree if Foldable or not.- C| C++| Java
  • check whether tree is Symmetric – C| C++| Java.
  • Check for Children-Sum in Binary Tree- C|C++| Java
  • Sum of all nodes in Binary Tree- C | C++ | Java
  • Lowest Common Ancestor in Binary Tree- C | C++ | Java

Introduction to Trees

Binary Trees

Binary Search Trees

Traversals

  • Traversal in Trees
  • Tree Traversals: Breadth-First Search (BFS) : C | C++ | Java
  • Tree Traversals: Depth First Search (DFS) : C | C++ | Java
  • Construct a Binary Tree from Postorder and Inorder

B – Trees

AVL Trees

  • AVL Trees
    • AVL Trees: Introduction
    • AVL Tree Insertion :  C | C++ | Java
    • AVL Tree Deletion : C | C++ | Java
    • Insertion in a Binary Tree (Level Order) – C | C++ | Java
    • Searching in Binary Tree – C | C++ | Java
    • Searching in a Binary Search Tree – C | C++ | Java

Complete Programs for Trees

  • Depth First Traversals – C | C++ | Java
  • Level Order Traversal – C | C++ | Java
  • Construct Tree from given Inorder and Preorder traversals – C | C++ | Java
  • Construct Tree from given Postorder and Inorder traversals – C | C++ | Java
  • Construct Tree from given Postorder and Preorder traversal – C | C++ | Java
  • Find size of the Binary tree – C | C++ | Java
  • Find the height of binary tree – C | C++ | Java
  • Find maximum in binary tree – C | C++ | Java
  • Check whether two tree are identical- C| C++| Java
  • Spiral Order traversal of Tree- C | C++| Java
  • Level Order Traversal LIne by Line – C | C++| Java
  • Hand shaking lemma and some Impotant Tree Properties.
  • Check If binary tree if Foldable or not.- C| C++| Java
  • check whether tree is Symmetric  C| C++| Java.
  • Check for Children-Sum in Binary Tree- C|C++| Java
  • Sum of all nodes in Binary Tree- C | C++ | Java
  • Lowest Common Ancestor in Binary Tree. C | C++ | Java