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Binary Tree Level Order Traversal

medium
Acceptance: 55%
Binary Tree

Perform a breadth-first traversal of a binary tree and return the node values grouped by depth level. Each level's values should be listed from left to right.

Examples

Example 1:
Input:root = [10,5,15,3,7,null,20]
Output:[[10],[5,15],[3,7,20]]
Example 2:
Input:root = [42]
Output:[[42]]

Hints

Related Problems

Maximum Depth of Binary TreeeasyInvert Binary TreeeasyValidate Binary Search TreemediumLowest Common Ancestor of a Binary TreemediumBinary Tree Zigzag Level Order Traversalmedium
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import java.util.*;

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> result = new ArrayList<>();
        if (root == null) return result;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> level = new ArrayList<>();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                level.add(node.val);
                if (node.left != null) queue.offer(node.left);
                if (node.right != null) queue.offer(node.right);
            }
            result.add(level);
        }
        return result;
    }
}
Time complexityO(n)
Space complexityO(n)