Reverse a Linked List

Step0 / 28

PhaseSetup

Nodes5

Result[]

Reverse Routine (Python)

2    def reverseList(self, head):
●        prev = None
4        curr = head
5 
6        while curr:
7            next_node = curr.next
8            curr.next = prev
9            prev = curr
10            curr = next_node
11 
12        return prev

Current Line (3): Initialize prev

Linked List Reversal

Start

Step

0 / 28

Phase

Setup

Reversed

Reversal Progress

Current Node

Phase

Setup

Reversed So Far

Reversed nodes appear here...

Press Next to initialize pointers.

Pointer State

prevNone

curr1

next_nodeNone

Why This Step Matters

Before each iteration: nodes before prev are reversed, nodes from curr onward are not.

Current Action

Initialize pointers: prev = None, curr = 1

Step Explanation

Start

Function Called

reverseList(head) starts. We set up prev and curr before touching any link.

> Phase: Setup
> Nothing is reversed yet.
> curr starts on the first node.
> Think of prev as reversed-so-far and curr as node-in-hand.

Unvisited

Current

Next Saved

Reversing

Done