binary-tree-level-order-traversal-ii.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

from collections import deque

class Solution:
    def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
        if not root:
            return []

        result = []

        queue = [root]

        while queue:
            old_queue, queue = queue, []

            result.append([n.val for n in old_queue])

            for node in old_queue:
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)

        return list(reversed(result))


    def levelOrderBottom(self, root):
        if not root:
            return []

        stack = [root]
        result = deque()

        while stack:
            result.appendleft([s.val for s in stack])
            old_stack = stack

            stack = []

            for node in old_stack:
                if node.left:
                    stack.append(node.left)
                if node.right:
                    stack.append(node.right)

        return list(result)