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

Approach

Solution

# 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]:
        prev = None
        curr = head
        while curr:
            next_ = curr.next
            curr.next = prev
            prev = curr
            curr = next_
        return prev

Explanation