Symmetric Tree

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