src/main/java/com/fishercoder/solutions/_82.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.ListNode;

/**
 * 82. 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.

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

 */
public class _82 {

    public ListNode deleteDuplicates(ListNode head) {
        if (head == null) {
            return head;
        }
        ListNode fakeHead = new ListNode(-1);
        fakeHead.next = head;
        ListNode pre = fakeHead;
        ListNode curr = head;
        while (curr != null) {
            while (curr.next != null && curr.val == curr.next.val) {
                curr = curr.next;
            }
            if (pre.next == curr) {
                pre = pre.next;
            } else {
                pre.next = curr.next;
            }
            curr = curr.next;
        }
        return fakeHead.next;
    }

}