Binary Tree Level Order Traversal - rFronteddu/general_wiki GitHub Wiki

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> l = new ArrayList<>();
        if (root == null) {
            return l;
        }
        
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        
        while (!q.isEmpty()) {
            int levelSize = q.size();
            
            List<Integer> currLevelList = new ArrayList<>();
            for (int i = 0; i < levelSize; i++) {
                var curr = q.poll();
                currLevelList.add(curr.val);
                if (curr.left != null) {
                    q.add (curr.left);
                }
                if (curr.right != null) {
                    q.add (curr.right);
                }
            }
            l.add (currLevelList);
        }

        return l;
    }
}