Level Order Traversal in Java
Level Order Traversal
Here we will Practice Level Order Traversal in Java programming using a clean, beginner friendly approach with algorithm, code, example, and complexity.
Level Order Traversal is one of the most important tree traversal techniques where nodes are visited level by level from left to right. It is also known as Breadth First Search (BFS) in trees.
What is Level Order Traversal?
Level Order Traversal means:
- Visit nodes level wise
- Start from the root
- Move left to right at each level
Example for Searching in a Binary Search Tree
Why Do We Use Level Order Traversal?
Level order traversal is useful for:
- Processing nodes level by level
- Finding minimum depth
- Printing tree structure
- Implementing heaps
- Solving shortest path problems in trees
Core Idea:
Level Order Traversal uses a Queue (FIFO):
- Insert nodes into queue
- Remove and process nodes
- Add their children to queue
Algorithm for Level Order Traversal in Java
Step by Step Algorithm for Level order traversal….
- If root is null, return
- Create an empty queue
- Add root to queue
- While queue is not empty:
Remove front node
Print/process it
Add left child (if exists)
Add right child (if exists)
Pseudocode
LevelOrder(root):
if root == null:
return
create queue
enqueue root
while queue not empty:
node = dequeue
process(node)
if node.left != null:
enqueue node.left
if node.right != null:
enqueue node.right 
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Java Code for Level Order Traversal
Code:
import java.util.*;
class Node {
int data;
Node left, right;
Node(int value) {
data = value;
left = right = null;
}
}
public class LevelOrderTraversal {
public static void levelOrder(Node root) {
if (root == null) return;
Queue queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
Node current = queue.poll();
System.out.print(current.data + " ");
if (current.left != null)
queue.add(current.left);
if (current.right != null)
queue.add(current.right);
}
}
public static void main(String[] args) {
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.left = new Node(4);
root.left.right = new Node(5);
root.right.right = new Node(6);
System.out.print("Level Order Traversal: ");
levelOrder(root);
}
}
Input:
1
/ \
2 3
/ \ \
4 5 6Output:
Level Order Traversal: 1 2 3 4 5 6
Each node is visited exactly once.
Queue may store all nodes at a level.
Conclusion
Common Insights:
- Level Order Traversal = BFS in trees
- Uses queue instead of recursion
- Important for level based problems
- Basis for heap and priority queue
Best Practices:
- Always check for null root
- Use Queue interface (LinkedList or ArrayDeque)
- Keep traversal iterative
- Avoid recursion for BFS
- Use traversal for debugging tree structure
Frequently Asked Questions
Answer:
Level Order Traversal in Java is a method of visiting all nodes of a tree level by level using a queue based approach.
Answer:
It uses a queue to process nodes in FIFO order, visiting each level from left to right before moving to the next level.
Answer:
The time complexity is O(n) because every node is visited once.
Answer:
Because it explores nodes breadth wise (level by level) instead of depth wise.
Answer:
It is used in heaps, shortest path problems, tree printing, and level based computations.
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