funcisSymmetric(root *TreeNode)bool { if root == nil { returntrue }
return isSymmetricHelper(root.Left,root.Right) }
funcisSymmetricHelper(left,right *TreeNode)bool { if left == nil || right == nil{ return left == right } if left.Val != right.Val{ returnfalse } return isSymmetricHelper(left.Left,right.Right) && isSymmetricHelper(left.Right,right.Left) }