Problem: Linked List Cycle II

Medium

30 min

Explore how to identify the starting node of a cycle in a linked list, applying an O(n) time and O(1) space solution. This lesson helps you understand cycle detection, analyze problem constraints, and implement efficient algorithms in a coding interview context.

Statement

Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null.

A cycle exists in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally, pos denotes the node’s index to which the tail’s next pointer is connected.

Constraints:

The number of the nodes in the list is in the range $[0, 10^4]$ .
$-10^5 \leq$ Node.value $\leq 10^5$
pos is - $1$ or a valid index in the linked list.

Note: The pos parameter isn’t passed as a parameter.

Problem: Linked List Cycle II

Medium

30 min

Statement

Given the head of a linked list, return the node where the cycle begins. If there is no cycle, return null.

Constraints:

The number of the nodes in the list is in the range $[0, 10^4]$ .
$-10^5 \leq$ Node.value $\leq 10^5$
pos is - $1$ or a valid index in the linked list.

Note: The pos parameter isn’t passed as a parameter.

Problem: Linked List Cycle II

Statement

Examples

Understand the problem

Try it yourself

Problem: Linked List Cycle II

Statement

Examples

Understand the problem

Try it yourself