The duplicate creates a cycle because two indices eventually lead to the same node. Floyd’s Tortoise and Hare algorithm detects that cycle without modifying the array. Resetting one pointer to the start lets you find the cycle entrance, which is the duplicate number.

The reverse-order representation makes the addition easier because the least significant digits appear first. This allows us to process the linked lists from left to right, just like digit-by-digit addition.

This problem is an extension of the classic linked list cloning problem. Along with the usual next pointer, every node also contains a random pointer that can point to any node in the list or be null.

The two-pointer technique is useful when a problem asks us to find a node relative to the end of a linked list. The dummy node simplifies edge cases, especially when the node being removed is the head.

Find the midpoint once. Reverse the second half once. Merge both halves once. Each node is visited only a constant number of times, making the solution both efficient and easy to reason about.

This problem demonstrates several important linked-list techniques: Using a dummy node to simplify list construction. Updating pointers without creating unnecessary nodes.

This is one of the most frequently asked linked list interview problems, and understanding the intuition behind the two-pointer approach will help you tackle many other linked list questions as well.

Linked lists are one of the most fundamental data structures, and reversing a linked list is a classic interview question. Although the problem is straightforward, it tests your understanding of pointers and how nodes are connected.

You are given the heads of two sorted linked lists, list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list.

Given the head of a singly linked list, our task is to reverse the list and return the reversed version. For example, if the input linked list is [1, 2, 3, 4, 5], the reversed list should be [5, 4, 3, 2, 1].