In last post we have seen the iterative method of post order traversal of a binary tree. In this post we see how to find an preorder traversal of a Binary tree.

Recursive solution:

void preOrderTraversal(TreeNode *root)
if (!root) return;
cout << root->data;

Iterative Solution:
• Push the root node to the stack.
• while stack is not empty
. • Pop a node from the stack, and enque It in the queue (or just print it, skip last step if you are just printing it).
. • Push its right child followed by its left child to the child stack.
• end while
• Now the Queue would have all the nodes ready to be traversed in pre-order. Deque the nodes from the Queue one by one and you will have the pre order traversal of the tree.

Below is the C++ program for the same:

void preOrderTraversalIterative(BinaryTree *root)
if (!root) return;
stack<BinaryTree*> s;
Queue<BinaryTree*> output;
while (!s.empty()) {
BinaryTree *curr =;
//Enque Current element in Output queue or just print
if (curr->right)
if (curr->left)
//skip this while loop if you were printting earlier
while (!output.empty()) {
cout << output.deque()->data << " ";
This works just magically, try an example yourself and you will see how it works.

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