partition List

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param head: The first node of linked list.
     * @param x: an integer
     * @return: a ListNode 
     */
    public ListNode partition(ListNode head, int x) {
        if(head == null){
            return head;
        }

        ListNode dummy1 = new ListNode(0);
        ListNode dummy2 = new ListNode(0);
        ListNode left = dummy1, right = dummy2;

        while(head !=null){
            if(head.val< x){
                left.next = head;
                left = left.next;
            }
            else{
                right.next = head;
                right = right.next;
            }
            head = head.next;
        }
        right.next =null;
        left.next = dummy2.next;

        
        return dummy1.next;
    }
}