LeetCode #82 Remove Duplicates from Sorted List II

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Problem

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

Examples

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

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

Solution

Method:

Time Complexity:

Space Complexity:

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def printList(self, head):
        while head:
            print(head.val, ' ', end='')
            head = head.next

    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return head

        dummy_head = ListNode(float('-inf'))
        dummy_head.next = head

        prev_valid_ptr = dummy_head
        current_ptr = head
        detect_ptr = head.next
        should_remove = False
        
        while current_ptr and detect_ptr:
            if current_ptr.val == detect_ptr.val:
                should_remove = True
                current_ptr = current_ptr.next
                detect_ptr = detect_ptr.next
                continue
            else:
                if should_remove is False:
                    prev_valid_ptr = prev_valid_ptr.next
        
                should_remove = False
                current_ptr = current_ptr.next
                detect_ptr = detect_ptr.next

        if should_remove is False:
            prev_valid_ptr.next = current_ptr
        else:
            prev_valid_ptr.next = None

        return dummy_head.next
    
# testcase 1 1->1->2->2
# head = ListNode(1)
# head.next = ListNode(1)
# head.next.next = ListNode(2)
# head.next.next.next = ListNode(2)
# Solution().printList((Solution().deleteDuplicates(head)))

# testcase 2 1->2->3->4
# head = ListNode(1)
# head.next = ListNode(2)
# head.next.next = ListNode(3)
# head.next.next.next = ListNode(4)
# Solution().printList((Solution().deleteDuplicates(head)))

Note

Beware of the continuous duplicates