Pattern concept

Step 1 of 33

Use ← → arrow keys

Code snippets

# Definition for a TreeNode.
class TreeNode:
   def __init__(self, val=0, left=None, right=None):
     self.val = val
     self.left = left
     self.right = right

# Return a list of list of nodes in the tree, organized by levels.
def level_order_traversal(root: TreeNode) -> List[str]:

  # Initialize a queue with the starting node.
  queue = deque([root])
  result = []

  while queue:
    level = []  # Track the current level's values.

    # Iterate through the queue's initial length.
    for _ in range(len(queue)):
      node = queue.popleft()  # Pop off the queue.

      # Save the current node value for this problem.
      level.append(node.val)

      # Add the child nodes to the queue.
      if node.left:
        queue.append(node.left)
      if node.right:
        queue.append(node.right)
    
    result.append(level)

  return result

How to identify

Does the problem involve any of these?

• Process the nodes by layers
  • Binary Tree Level Order Traversal from Right to Left: Find the level with the most nodes.
  • Max Width of Binary Tree: Find the level with the most nodes.
  • Binary Tree Zigzag Traversal: Visit nodes level by level in alternating order.
  • Symmetric Tree: Compare left and right nodes on the same layer to test for symmetry.
• Operating on nodes based on their level in the tree
  • Cousins in a Binary Tree: Determine if nodes are on the same level but not siblings.