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.

partition.java

/*
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.

You should preserve the original relative order of the nodes in each of the two partitions.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.
*/
public ListNode partition(ListNode head, int x) {
    ListNode root = new ListNode(-1);
    ListNode pivot = new ListNode(x);
    ListNode root_last = root, pivot_last = pivot;

    ListNode cur_node = head;
    while (cur_node != null) {
        ListNode next = cur_node.next;
        if (cur_node.val < x) {
            root_last.next = cur_node;
            root_last = cur_node;
        } else {
            pivot_last.next = cur_node;
            pivot_last = cur_node;
            pivot_last.next = null;
        }
        cur_node = next;
    }
    root_last.next = pivot.next;

    return root.next;
}