Sort Linked List

LinkListSort

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode sortList(ListNode head) {
        if(head==null || head.next==null){
            return head;
        }
        ListNode left = head;
        ListNode right = null;
        ListNode p1 = head;
        int count =0;
        while(p1!=null){
            count++;
            p1=p1.next;
        }
        int halfCount =0;
        int middle = count/2;
        p1=head;
        while(p1!=null){
            halfCount++;
            ListNode next = p1.next;
            if(halfCount==middle){
                right = next;
                p1.next = null;
            }
            p1=p1.next;
        }
        ListNode leftHalf  = sortList(left);
        ListNode rightHalf = sortList(right);
        ListNode mergeList = merge(leftHalf,rightHalf);
        return mergeList;
    }
    
    private ListNode merge(ListNode left, ListNode right){
        ListNode p1 = left;
        ListNode p2 = right;
        ListNode fakeHead = new ListNode(100);
        ListNode nNext = fakeHead;
        while( p1!=null || p2!=null ){
            if(p1==null){
                nNext.next = new ListNode(p2.val);
                p2 = p2.next;
                nNext = nNext.next;
            }else if(p2==null){
                nNext.next = new ListNode(p1.val);
                p1 = p1.next;
                nNext = nNext.next;
            }else{
                if(p1.val<p2.val){
                    nNext.next = new ListNode(p1.val);
                    p1 = p1.next;
                    nNext = nNext.next;
                }else if(p1.val==p2.val){
                    nNext.next = new ListNode(p1.val);
                    nNext = nNext.next;
                    p1 = p1.next;
                    nNext.next = new ListNode(p2.val);
                    p2 = p2.next;
                    nNext = nNext.next;
                }else{
                    nNext.next = new ListNode(p2.val);
                    p2 = p2.next;
                    nNext = nNext.next;
                }
            }
        }
        return fakeHead.next;
    }
}