### Binary Tree Level Order Traversal - The Coding Shala

Last Updated: 19-Jan-2021
Home >> Data Structures >> Binary Tree Level Order Traversal

In this post, we will learn how to Traverse a Binary Tree in Level Order.

## Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

Example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9  20
/  \
15   7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]

## Level Order Traversal of Binary Tree in Java

Approach 1

Using Queue[BFS]. Iterative Solution.

Java Program:

```/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> ans = new ArrayList<>();
if(root == null) return ans;
queue.offer(root);
while(!queue.isEmpty()){
int size = queue.size();
List<Integer> tmp = new ArrayList<>();
for(int i=0; i< size; i++){
TreeNode curr = queue.poll();
if(curr.left != null) queue.offer(curr.left);
if(curr.right != null) queue.offer(curr.right);
}
}
return ans;
}
}
```

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