Partition List

# Definition for singly-linked list.
class ListNode:
     def __init__(self, x):
         self.val = x
         self.next = None

class 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