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LeetCode 82 Remove Duplicates From Sorted List II - Medium

82. Remove Duplicates from Sorted List II

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82. Remove Duplicates From Sorted List II — Medium

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Problem

  1. 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.

Return the linked list sorted as well.

Example 1:

Input: 1->2->3->3->4->4->5 Output: 1->2->5 Example 2:

Input: 1->1->1->2->3 Output: 2->3

Solution

### 三指针的Linked List版本，利用dummy node 的帮助构造，prev， curr，next三种指针：
 
# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        dummy = ListNode(None, head)
        prev = dummy
        curr = head
        if head is None or head.next is None:
            return dummy.next
        next = head.next
        # prev , curr , next
        while next:
            if curr.val == next.val:
                # remember to check edge, ensure next.next exist
                while next and curr.val == next.val:
                    next = next.next
                prev.next = next
                curr = prev
                next = curr.next
            
            else:
                prev = prev.next
                
            # check edge, ensure curr.next,and next.next exist
            if prev.next:
                curr = curr.next
                next = next.next
        return dummy.next

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