# Definition for singly-linked list.class ListNode:     def __init__(self, x):         self.val = x         self.next = Noneclass Solution:    # @param head, a ListNode    # @param x, an integer    # @return a ListNode    def partition(self, head, x):        if head==None:            return head
        less_node_list=ListNode(0)        greater_node_list=ListNode(0)        head1=less_node_list        head2=greater_node_list
        while head!=None:            if head.val<x:                head1.next=ListNode(head.val)                head1=head1.next            else:                head2.next=ListNode(head.val)                head2=head2.next            head=head.next
        head1.next=greater_node_list.next        return less_node_list.next