class Solution:
    def isSubtree(self, s: TreeNode, t: TreeNode) -> bool:
        #  both None
        if s is None and t is None:
            return True
        
        # any None
        if s is None or t is None:
            return False

        # if same return 
        if self.is_same(s, t):
            return True

        # recursive
        return self.isSubtree(s.left, t) or self.isSubtree(s.right, t)
    
    def is_same(self, s, t):
        # both None
        if s is None and t is None:
            return True

        # any None
        if s is None or t is None:
            return False

        # compare s.val and t.val
        if s.val != t.val:
            return False
        return self.is_same(s.left, t.left) and self.is_same(s.right, t.right)