Reverse Linked List

Problem

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

Examples:

// 1 -> 2 -> 3 -> 4 -> 5 -> NULL
reverseList([1,2,3,4,5])
// [5,4,3,2,1]
// 5 -> 4 -> 3 -> 2 -> 1 -> NULL

reverseList([3,4,5])
// returns [5,4,3]
reverseList([1])
// returns [1]

Time Complexity

The time complexity of reversing a linked list is O(n), where n is the number of nodes in the list. This can be achieved either iteratively or recursively.