144. Binary Tree Preorder Traversal.py

# 144. Binary Tree Preorder Traversal

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def preorderTraversal(self, root):
        res = []
        if root:
            res.append(root.val)
            res = res + self.preorderTraversal(root.left)
            res = res + self.preorderTraversal(root.right)
        return res