[LintCode] #96 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) {
        // write your code here
        ListNode leftDummy = new ListNode(-1);
        ListNode rightDummy = new ListNode(-1);
        ListNode leftHead = leftDummy;
        ListNode rightHead = rightDummy;
        while (head != null) {
            if (head.val < x) {
                leftHead.next = head;
                leftHead = leftHead.next;
            } else {
                rightHead.next = head;
                rightHead = rightHead.next;
            }
            head = head.next;
        }
        leftHead.next = rightDummy.next;
        rightHead.next = null; //Attn!!!!!
        return leftDummy.next;
    }
}