I tried to test a leetcode solution on my local PC (WSL, python3) to have a better understanding of the problem

from https://leetcode.com/problems/same-tree/discuss/2594714/python-recurse-in-same-function I modified it as

from typing import Optional
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

class Solution:
    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
        
        if not p and not q:
            return True

        elif (p and not q) or (q and not p):
            return False

        return (
            self.isSameTree(p.left, q.left) and
            (p.val == q.val) and
            self.isSameTree(p.right, q.right)
        )

print(Solution.isSameTree([1,2,3],[1,2,3]))        

I got (binary_tree.py is the name of the file for the above code)

Traceback (most recent call last):
  File "binary_tree.py", line 24, in <module>
    print(Solution.isSameTree([1,2,3],[1,2,3]))
TypeError: isSameTree() missing 1 required positional argument: 'q'

Seems I have a very basic issue in using python class. But, what is the problem and how to fix it?

CodePudding user response：

TLDR

You need to instantiate the Solution class instance before calling the class function. i.e.,

solution = Solution()
tree1 = TreeNode(1, TreeNode(2), TreeNode(3))
tree2 = TreeNode(1, TreeNode(2), TreeNode(3))
print(solution.isSameTree(tree1, tree2))

Or, you should add @classmethod or @staticmethod decorator on the isSameTree function.

Explanation

The error stack told you that TypeError: isSameTree() missing 1 required positional argument: 'q'. In other words. isSameTree() needs three required arguments while you only pass two of them(self, p). The first list of your arguments is considered as a self.

By instantiating a Solution class instance, calling with it will pass self as an argument automatically. Or you can add @classmethod to pass cls automatically without instantiating a class instance. @staticmethod has similar effect but works differently. Check answers under this question for more information: Difference between @staticmethod and @classmethod

Also, passing lists into isSameTree doesn't work either. You should build TreeNodes by TreeNode class.