Print by level order

levelorderprint.py

def levelOrder(root):
    """
    :type root: TreeNode
    :rtype: List[List[int]]
    """
    if root:
      queue = [root]
      res = []
      while queue:
        tmp = []
        next = []
        for node in queue:
          tmp.append(node.val)
          if node.left:
            next.append(node.left)
          if node.right:
            next.append(node.right)
        res.append(tmp)
        queue = next
      return res
    return []