litncode-medium-Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

 

Example

Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

 

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param ListNode head is the head of the linked list
     * @return: ListNode head of the linked list
     */
    public static ListNode deleteDuplicates(ListNode head) {
        // write your code here
        
        if(head == null || head.next == null)
            return head;
        
        ListNode fakehead = new ListNode(0);
        fakehead.next = head;
        
        ListNode p1 = fakehead;
        ListNode p2 = head;
        
        while(p2 != null && p2.next != null){
            while(p2 != null && p2.next != null && p2.val != p2.next.val){
                p1 = p1.next;
                p2 = p2.next;
            }
            
            if(p2.next == null)
                break;
            
            while(p2 != null && p2.next != null && p2.val == p2.next.val){
                p2 = p2.next;
                
                if(p2 != null && p2.next != null && p2.val != p2.next.val){
                    p2 = p2.next;
                }
            }
            
            if(p2.next == null){
                p1.next = null;
            }
            else{
                p1.next = p2;
                p2 = p2.next;
                p1 = p1.next;
            }
        }
        
        return fakehead.next;
    }
}