101. Symmetric Tree

class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        if not root:
            return True
 
        def recurse(ln, rn):
            if not ln and not rn: return True
            if ln and rn:
                if ln.val == rn.val:
                    return recurse(ln.left, rn.right) and recurse(rn.left, ln.right)
            # if one of them is None, or values are not equal
            return False
        
        return recurse(root.left, root.right)

• we do a recursion on the binary-tree with two nodes in the arguments.
• start with recursing on the left and right subtrees, because it doesn’t matter what the value of root is.

Categories:: binary-tree, tree, recursion