栈和队列_leetcode107

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

class Solution(object):
    def levelOrderBottom(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        if not root :
            return res

        queue = []
        queue.append(root)

        while queue:
            level = []

            for i in range(len(queue)):
                node = queue.pop(0)
                level.append(node.val)

                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)

            res.append(level)
        return res[::-1]