LeetCode: Partition List

LeetCode: Partition List 

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/**
 * Description: Given a linked list and a value x, partition it such that all nodes less than x come before nodes
 * greater than or equal to x.
 * <p/>
 * You should preserve the original relative order of the nodes in each of the two partitions.
 * <p/>
 * For example, Given 1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5.
 *
 * @author hzhou
 */
public class PartitionList {
    public ListNode partition(ListNode head, int x) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode preHead = new ListNode(0);
        preHead.next = head;
        ListNode pre, cursor;
        pre = preHead;
        cursor = head;
        while (cursor != null && cursor.val < x) {
            pre = cursor;
            cursor = cursor.next;
        }
        // pre is the end of left side
        ListNode crt = pre;
        while (cursor != null) {
            while (cursor != null && cursor.val >= x) {
                crt = cursor;
                cursor = cursor.next;
            }
            if (cursor != null) {
                crt.next = cursor.next;
                cursor.next = pre.next;
                pre.next = cursor;
                pre = pre.next;
                cursor = crt.next;
            }
        }
        return preHead.next;
    }
    @Test
    public void test() {
        //1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5.
        ListNode head = new ListNode(1);
        head.next = new ListNode(4);
        head.next.next = new ListNode(3);
        head.next.next.next = new ListNode(2);
        head.next.next.next.next = new ListNode(5);
        head.next.next.next.next.next = new ListNode(2);
        ListNode result = partition(head, 3);
    }
}