My AC Code ,is there a better method ?
 public boolean checkSymmetric(TreeNode lsubTree,TreeNode rsubTree){\n        if(lsubTree==null&&rsubTree==null) return true;\n        else if(lsubTree!=null&&r
     public boolean checkSymmetric(TreeNode lsubTree,TreeNode rsubTree){\n        if(lsubTree==null&&rsubTree==null) return true;\n        else if(lsubTree!=null&&rsubTree==null) return false;\n        else if(lsubTree==null&&rsubTree!=null) return false;\n        else if(lsubTree.val!=rsubTree.val) return false;\n        boolean lt=checkSymmetric(lsubTree.left,rsubTree.right);\n        boolean rt=checkSymmetric(lsubTree.right,rsubTree.left);\n        return lt&&rt;\n    }\n    public boolean isSymmetric(TreeNode root) {\n        if(root==null) return true;\n        return checkSymmetric(root.left,root.right);\n    }
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