Reverse a Linked List

Problem Statement:
Given the head of a linked list, reverse the list and return the new head.

Example:
Input: 1 → 2 → 3 → 4 → 5
Output: 5 → 4 → 3 → 2 → 1

Approach:
We traverse the list and reverse the direction of links using three pointers:

• previous node
• current node
• next node Code:

class ListNode:
def init(self, val=0, next=None):
self.val = val
self.next = next

def reverseList(head):
prev = None
current = head

while current:
    next_node = current.next
    current.next = prev
    prev = current
    current = next_node

return prev

Explanation:
Each node’s next pointer is reversed to point to the previous node. At the end, the previous pointer becomes the new head.

Time Complexity:
O(n)

Space Complexity:
O(1)