206. Reverse Linked List

206. Reverse Linked List

 

 

Given the head of a singly linked list, reverse the list, and return the reversed list.

 

Example 1:

 

Input: head = [1,2,3,4,5]

Output: [5,4,3,2,1]

Example 2:

 

Input: head = [1,2]

Output: [2,1]

Example 3:

Input: head = []

Output: []

 

Constraints:

• The number of nodes in the list is the range [0, 5000].
• -5000 <= Node.val <= 5000

 

class Solution:
    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        cur = head
        prev = None
        while cur:
            tmp=cur.next
            cur.next=prev
            prev=cur
            cur=tmp
        return prev