Leetcode 107. Binary Tree Level Order Traversal II

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/

We can use ordinary level order traversal and reverse the result.

Solution:

# T:O(n) S:O(n)
class Solution:
    # @param {TreeNode} root
    # @return {integer[][]}
    def levelOrder(self, root, level, res):
        if root:
            if len(res) < level + 1:
                res.append([])
            res[level].append(root.val)
            self.levelOrder(root.left, level + 1, res)
            self.levelOrder(root.right, level + 1, res)
    def levelOrderBottom(self, root):
        res = []
        self.levelOrder(root, 0, res)
        res.reverse()
        return res

Run Time: 76 ms