# Binary Tree PreOrder traversal in java

If you want to practice data structure and algorithm programs, you can go through top 100+ data structure and algorithm interview questions.

This is 2nd part of java binary tree tutorial.

In this post, we will see about PreOrder binary tree traversal in java.

## PreOrder traversal:

In PreOrder traversal,each node is processed before either of its sub-trees.In simpler words,Visit each node before its children.
Steps for PreOrder traversal are:
• `Visit` the node.
• Traverse the `left subtree` in PreOrder.
• Traverse the `right subtree` in PreOrder.

There can be two ways of implementing it

• Recursive
• Iterative

Recursive solution:
Recursive solution is very straight forward.Below diagram will make you understand recursion better.

Code for recursion will be:

Iterative solution:
For recursion, we use implicit stack. So here to convert recursive solution to iterative, we will use explicit stack.
Steps for iterative solution:

1. Create empty `stack` and pust root node to it.
2. Do the following when `stack` is not empty
• Pop a node from `stack` and print it
• Push `right child` of popped node to `stack`
• Push `left child` of popped node to stack

We are pushing right child first, so it will be processed after left subtree as Stack is LIFO.

Example:
Lets say your binary tree is :

Lets create java program for PreOrder traversal:

Run above program and you will get following output:

Using Recursive solution:
40 20 10 30 60 50 70
————————-
Using Iterative solution:
40 20 10 30 60 50 70

## Java Binary tree tutorial:

Please go through java interview programs for more such programs.

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