The Concept

Reversing a singly linked list is a classic pointer-manipulation exercise. To reverse the list, we iterate through the nodes and redirect the next pointer of each node to point to its predecessor (prev) instead of its successor.

We maintain three pointers:

  • prev: Points to the node before the current one (initially None).
  • curr: Points to the node we are currently processing (initially head).
  • next: Temporarily stores the node after curr before we rewrite curr.next.

Code Implementation

Below is the standard iterative implementation of Reverse Linked List:

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  • Time Complexity: O(N) since we visit each of the N nodes exactly once.
  • Space Complexity: O(1) auxiliary space as we only modify node pointers in-place.

Interactive Lab: Reverse Linked List

Step through node traversals and pointer redirects in real-time. Watch how list links flip sequentially:

Key Takeaway

reversing pointers sequentially requires a temporary variable to hold the upcoming node (next = curr.next). Reversing in-place runs in linear time with zero extra heap allocations, making it highly optimal.