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 83. Remove Duplicates from Sorted List

Easy

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Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

 

Example 1:

Input: head = [1,1,2]
Output: [1,2]

Example 2:

Input: head = [1,1,2,3,3]
Output: [1,2,3]

 

Constraints:

• The number of nodes in the list is in the range [0, 300].
• -100 <= Node.val <= 100
• The list is guaranteed to be sorted in ascending order.

# Definition for singly-linked list.

# class ListNode:

#     def __init__(self, val=0, next=None):

#         self.val = val

#         self.next = next

class Solution:

    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:

        #設定兩個快慢指針

        if head == None:

            return None

        slow=head   #讓慢指針指向head頭部,初始化慢指針

        fast=head.next #快指針指向下一項

       

       

        while fast:#快指針走遍一次

            if slow.val == fast.val:

    '''等於下一項時,不指定慢指針下一項,讓快指針跳到下一輪迴圈'''

                fast=fast.next

            else:

    '''不相等時,讓慢指針指向該項元素,快指針在繼續往右判斷下一個元素'''

                slow.next=fast

                slow=slow.next

                fast=fast.next

#走遍迴圈後 慢指針還沒走完,但實際上已經走到最尾巴了,所以下一項不存在

#next會指向None

        slow.next=None

        return head