分别比较pRoot1.left,pRoot2.right 和 pRoot1.right,pRoot2.left

	boolean isSymmetrical1(TreeNode pRoot1,TreeNode pRoot2) {
        if(pRoot1 == null && pRoot2 == null){
            return true;
        }
        if(pRoot1 == null || pRoot2 == null || pRoot1.val != pRoot2.val){
            return false;
        }
        return isSymmetrical1(pRoot1.left,pRoot2.right) && isSymmetrical1(pRoot1.right,pRoot2.left);
    }