public boolean isSym(TreeNode n1,TreeNode n2){
		if(n1==null&&n2==null){
			return true;
		}else if((n1==null&&n2!=null) || (n1!=null&&n2==null)){
			return false;
		}else{
			if(n1.val==n2.val&&isSym(n1.left, n2.right)&&isSym(n1.right,n2.left)){
				return true;
			}
			return false;
		}
	}