/*
 * @lc app=leetcode id=86 lang=java
 *
 * [86] Partition List
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode partition(ListNode head, int x) {
        ListNode tf = new ListNode(0), 
        tb = new ListNode(0);
        tf.next = null;
        tb.next = null;
        ListNode cur = head, tailf = tf, tailb = tb;
        while(cur != null) {
            if(cur.val < x) {
                tailf.next = cur;
                cur = cur.next;
                tailf = tailf.next;
                tailf.next = null;
            } else {
                tailb.next = cur;
                cur = cur.next;
                tailb = tailb.next;
                tailb.next = null;
            }
        }
        tailf.next = tb.next;
        return tf.next;
    }
}
// @lc code=end