Leetcode-Problems/86. Partition List at master · alexkoby/Leetcode-Problems · GitHub

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/**
 * 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) {
        int target = x;
        ListNode firstTarget = null, currentTarget = null
            , firstLower = null, currentLower = null, mover;
        if(head == null){
            return null;
        }
        mover = head;
        while(mover != null){
            if(mover.val < target){
                if(firstLower == null){
                    firstLower = mover;
                    currentLower = mover;
                }
                else{
                    currentLower = currentLower.next = mover;
                }
            }
            else{
                if(firstTarget == null){
                    firstTarget = mover;
                    currentTarget = mover;
                }
                else{
                    currentTarget = currentTarget.next = mover;
                }
            }
            mover = mover.next;
        }

        if(firstLower != null){
            if(firstTarget != null){
                currentLower.next = firstTarget;
                currentTarget.next = null;
            }
            return firstLower;
        }
        else{ //firstLower == null -- just attach middle
            return firstTarget;
        }
    }
}