102. Binary Tree Level Order Traversal

102. Binary Tree Level Order Traversal

BFS

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:        
        if not root:
            return []
        queue = deque([root])
        res = defaultdict(list)
        level = 0
        while queue:
            size = len(queue)
            for i in range(size):
                node = queue.popleft()
                res[level].append(node.val)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            level += 1

        return res.values()

DFS

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        res = defaultdict(list)
        if not root:
            return []

        def helper(node, level):            
            res[level].append(node.val)

            if node.left:
                helper(node.left, level + 1)
            if node.right:
                helper(node.right, level + 1)

        helper(root, 0)
        return res.values()