$ cat ./coding/144-binary-tree-preorder-traversal.md

────────────────────────────────────────────────────────────

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: TreeNode) -> List[int]:
        if not root:
            return []
        res = []
        res.append(root.val)
        res.extend(self.preorderTraversal(root.left))
        res.extend(self.preorderTraversal(root.right))
        return res

$ ls ./coding/ | grep -v 144-binary-tree-preorder-traversal