链表专题 - leetcode83. Remove Duplicates from Sorted List

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83. Remove Duplicates from Sorted List

题目描述

移除有序链表的重复结点

例子

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

解法
看到链表题，想到递归。
刚开始想用非递归写，发现有点绕。
[解法1] - 递归解法
[解法2] - 非递归，参照递归的思想

解法1
递归，截止条件-链表为空/只有一个元素。判断head和head.next是否相等，若相等，递归操作head.next；否则, 返回head

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

class Solution(object):
    def deleteDuplicates(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head or not head.next:
            return head
        
        if head.val == head.next.val:
            return self.deleteDuplicates(head.next)
        head.next = self.deleteDuplicates(head.next)
        return head

解法2
非递归，将递归改造成非递归。外面套一层while， 内部p = p.next.
为代码简洁起见，引入dummy指针pNode

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

class Solution(object):
    def deleteDuplicates(self, head):
        if not head or not head.next:
            return head
            
        pNode = ListNode(-1)
        pHead = pNode
        p = head
        while p:
            while p.next and p.val == p.next.val:
                p = p.next
            pNode.next = p
            pNode = pNode.next
            p = p.next
        return pHead.next