_86.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.ListNode;

/**
 * 86. Partition List
 *
 * 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 class _86 {

    public ListNode partition(ListNode head, int x) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode left = new ListNode(0);
        ListNode right = new ListNode(0);
        ListNode less = left;
        ListNode greater = right;
        while (head != null) {
            if (head.val < x) {
                less.next = head;
                less = less.next;
            } else {
                greater.next = head;
                greater = greater.next;
            }
            head = head.next;
        }
        greater.next = null;
        less.next = right.next;
        return left.next;
    }

}