反转链表【链表】

Problem: 206. 反转链表

思路 & 解题方法

简单链表

复杂度

时间复杂度:

$O(n)$

空间复杂度:

$O(n)$

Code

# 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: Optional[ListNode]) -> Optional[ListNode]:
        if not head:
            return None
        ans = ListNode(head.val, None)
        head = head.next
        while head:
            p = ListNode(head.val, ans)
            ans = p
            head = head.next
        
        return ans