[LeetCode]题解（python）：107-Binary Tree Level Order Traversal II

# 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]]
        """
        ans = []
        def bfs(root,level):
            if root != None:
                if len(ans) < level + 1:
                    ans.append([])
                ans[level].append(root.val)
                bfs(root.left,level + 1)
                bfs(root.right,level + 1)
        bfs(root,0)
        ans.reverse()
        return ans