# Is there any error in it,please tell me

• ``````public boolean isSymmetric(TreeNode root) {
if(root == null) return true;
TreeNode tmp = reverse(root);
if(tmp == root){
return true;
}
return false;
}
private TreeNode reverse(TreeNode root){
if(root == null) return root;
TreeNode tmp = root.left;
root.left = root.right;
root.right = tmp;
reverse(root.left);
reverse(root.right);
return root;
}``````

• You code seems reverse any nodes in the tree, when it is a leaf node the reverse will return null.
How could you use this to tell if a tree is a symmetric tree?

Here is my solution, if a tree is a symmetric tree, its left subtree and its right subtree shoudl be symmetric to each other

``````public class Solution {
public boolean isSymmetricSubTree(TreeNode left, TreeNode right){
if(left==null&&right==null) return true;
if(left==null&&right!=null||right==null&&left!=null) return false;
if(left.val!=right.val) return false;
return isSymmetricSubTree(left.left, right.right)&&isSymmetricSubTree(left.right,right.left);
}
public boolean isSymmetric(TreeNode root) {
if(root==null) return true;
return isSymmetricSubTree(root.left,root.right);
}
}``````

• for this code: if(tmp == root)

I think you want to compare the val of leave nodes, but you are actually compare two addresses.

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