[LeetCode By Python]107. Binary Tree Level Order Traversal II

タイトル:
Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
For example: Given binary tree  [3,9,20,null,null,15,7] ,

    3
   / \
  9  20
    /  \
   15   7

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

daコード＋デバッグ:

# 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]]
        """
        results = []
        if root == None:
            return results
        curr_level = [root]
        while curr_level:
            curr_result = []
            next_level = []
            for i in curr_level:
                curr_result.append(i.val)
                if i.left:
                    next_level.append(i.left)
                if i.right:
                    next_level.append(i.right)
            results.append(curr_result)
            curr_level = next_level
        results.reverse()
        return results


if __name__ == '__main__':
    l1_1 = TreeNode(1)
    l1_2 = TreeNode(2)
    l1_3 = TreeNode(3)

    l1_1.left = l1_2
    l1_1.right = l1_3

    l3 = Solution().levelOrderBottom(l1_1)
    print l3