6_in-place-reversal-of-a-linked-list

In-place reversal of a Linked List

When to use

For problems which requires us to reverse the whole linked list or partial of the linked list (sub list) in-place, i.e. using the existing node objects and without using extra memory.

Pseudo code

let prev = null;
let current = head;
while (current) {
  const next = current.next;
  current.next = prev;
  prev = current;
  current = next;
}
return prev;

The key is to remember:

• in every loop we only handle the pointer reversal between current node and prev, i.e. current.next = prev.
• after reversal, the prev pointer is the start of the reversed linked list, current is the the next pointer of the original end (e.g. null)