Leetcode 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.

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解题思路： 

关键是要设置一个dummy作为链表的开始。开始一直想用两个指针，但是一直混乱。看了答案后，答案只用了一个指针，思路一样。关键要理清楚。

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Java code :

1.

 public ListNode deleteDuplicates(ListNode head) {
        if(head == null) {
            return null;
        }
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode p1 = dummy;

        while(p1.next!= null && p1.next.next !=null) {
            if(p1.next.val == p1.next.next.val) {
                int value = p1.next.val;
                while(p1.next!= null && value == p1.next.val) {
                    p1.next = p1.next.next;
                }
            }else {
                p1 = p1.next;
            }
        }
        return dummy.next;
    }Reference:

2. 九章算法又做了一遍，思路完全一样。2016.01.18

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

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Reference:

1. http://www.programcreek.com/2014/06/leetcode-remove-duplicates-from-sorted-list-ii-java/