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Most people do not understand the knowledge points of this article "python how to reverse the linked list", so the editor summarizes the following contents, detailed content, clear steps, and has a certain reference value. I hope you can get something after reading this article. Let's take a look at this "how to reverse the linked list python" article.

[title]

Reverses a single linked list.

Example:

Enter: 1-> 2-> 3-> 4-> 5-> NULL

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

Advanced:

You can iterate or recursively reverse the linked list. Can you solve the problem in two ways?

[ideas]

Use three pointers p, Q, r to point to three adjacent nodes, where p.next is qmenq.next is r.

Modify the pointer to Q and move the three pointers p, Q and r, that is, q.next = pforce p = Q, Q = r r = r.next. Continuous circulation, and pay attention to modify head.next and head, the list can be flipped.

[code]

Python version

# Definition for singly-linked list.

# class ListNode:

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

# self.val = val

# self.next = next

Class Solution:

Def reverseList (self, head: ListNode)-> ListNode:

# head is empty

If not head:

Return head

# p, Q, r are three adjacent nodes

# q.next points to p, while three pointers move backward

P, Q, r = head, head.next, head

While q:

R = q.next

Q.next = p

P = Q

Q = r

# modify head.next and head

Head.next = None

Head = p

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