3 lines clean Python


  • 0

    The key idea is we need to check if L.val == R.val only when L and R are not None.

    class Solution(object):
        def isSymmetric(self, root):
            """
            :type root: TreeNode
            :rtype: bool
            """
            def helper(L, R):
                return L.val == R.val and helper(L.left, R.right) and \
                       helper(L.right, R.left) if L and R else L == R == None
            return helper(root, root)
    

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