Bug Report for serialize-and-deserialize-binary-tree

[pranav1233]

Bug Report for https://neetcode.io/problems/serialize-and-deserialize-binary-tree

Please describe the bug below and include any steps to reproduce the bug or screenshots if possible

for the below code, I am able to submit my solution and it actually gets accepted. But there is a logical error in the deserialize section where I am not actually returning anything from the recursive function, but somehow I am able to "return root" which I haven't defined outside the recursive function. It should throw an error.

class Codec:

# Encodes a tree to a single string.
def serialize(self, root: Optional[TreeNode]) -> str:
    res=[]

    def dfs(node):
        if not node:
            res.append("N")
            return
        res.append(str(node.val))
        dfs(node.left)
        dfs(node.right)
    dfs(root)
    return ",".join(res)
    
# Decodes your encoded data to tree.
def deserialize(self, data: str) -> Optional[TreeNode]:
    val=data.split(",")
    i=0

    def dfs():
        nonlocal i
        if val[i] == "N":
            i+=1
            return None
        root=TreeNode(int(val[i]))
        i+=1
        root.left=dfs()
        root.right=dfs()
    dfs()

    return root