144. Binary Tree Preorder Traversal

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

class Solution:
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res = [] 
        
        def got_val(root):
            if root:
                res.append(root.val)
                if root.left:
                    got_val(root.left)
                if root.right:
                    got_val(root.right)
            else:
                pass
        got_val(root)
        return res