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/**
 * 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 Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        // pointer
        ListNode prev = dummy;
        ListNode curr = head;
        while (curr != null){
            if (curr.next != null && curr.val == curr.next.val) {
                int val = curr.val;
                while(curr != null && curr.val == val) {
                    curr = curr.next;
                }
                prev.next = curr;
            } else {
                prev = curr;
                curr = curr.next;
            }
        }
        return dummy.next;
    }
}

/**
 * Given a sorted linked list, delete all duplicates such that each element appear only once.
 * For example,
 * Given 1->1->2, return 1->2.
 * Given 1->1->2->3->3, return 1->2->3.
 */

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution{
    public ListNode deleteDuplicates(ListNode head) {
        ListNode curr = head;
        while(curr != null && curr.next != null){
            if(curr.val == curr.next.val)
                curr.next = curr.next.next;
            else
                curr = curr.next;
        }
        return head;
    }
    
}