86. Partition List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode partition(ListNode head, int x) {
      ListNode dummy1 = new ListNode(-1);
      ListNode dummy2 = new ListNode(-1);
      ListNode cur1 = dummy1;
      ListNode cur2 = dummy2;
      ListNode cur = head;
      
      while( cur != null ){
        if( cur.val < x){
          cur1.next = cur;
          cur1 = cur1.next;
        }else{
          cur2.next = cur;
          cur2 = cur2.next;
        }
        cur = cur.next;
      }
      
      cur2.next = null;
      cur1.next = dummy2.next;
      return dummy1.next;
    }
}

 

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.

Example:

Input: head = 1->4->3->2->5->2, x = 3
Output: 1->2->2->4->3->5