PU Binary Tree Right Side View

   1            <---
 /   
2     3         <---
      
  5     4       <---

# 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 rightSideView(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root: return []
        l = [root]
        res = []
        while l:
            res.append(l[-1].val)
            r = []
            for node in l:
                if node.left: r.append(node.left)
                if node.right: r.append(node.right)
            l = r
        return res

# 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 rightSideView(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root: return []
        def preorder(root, res, level):
            if level == len(res):
                res.append(root.val)
            if root.right: preorder(root.right, res, level + 1)
            if root.left: preorder(root.left, res, level + 1)
        res = []
        preorder(root, res, 0)
        return res