Detect Cycle in Linked List Floyd's Algorithm in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind Floyd's Cycle Detection Algorithm in a linked list?

Floyd's Algorithm uses two pointers moving at different speeds (slow and fast). If there is a cycle, the fast pointer will eventually meet the slow pointer inside the cycle.

beginner

In Floyd's Cycle Detection Algorithm, what are the speeds of the two pointers?

The slow pointer moves one step at a time, while the fast pointer moves two steps at a time.

intermediate

Why does the fast pointer eventually meet the slow pointer if a cycle exists?

Because the fast pointer moves faster inside the cycle, it will lap the slow pointer and meet it at some node within the cycle.

beginner

What does it mean if the fast pointer reaches the end (null) in Floyd's Algorithm?

It means there is no cycle in the linked list because the fast pointer can move freely to the end without looping back.

intermediate

How can you find the starting node of the cycle after detecting a cycle using Floyd's Algorithm?

After detecting a cycle, reset one pointer to the head and move both pointers one step at a time. The node where they meet is the start of the cycle.

In Floyd's Cycle Detection Algorithm, what happens if the fast pointer reaches null?

A A cycle is detected

B The slow pointer moves faster

C There is no cycle in the linked list

D The algorithm restarts

If the fast pointer reaches null, it means the list ends and no cycle exists.

What is the speed difference between the two pointers in Floyd's Algorithm?

A Both move 2 steps

B Slow moves 1 step, fast moves 2 steps

C Slow moves 2 steps, fast moves 1 step

D Both move 1 step

The slow pointer moves one step at a time, and the fast pointer moves two steps at a time.

What does it mean if the slow and fast pointers meet inside the linked list?

A A cycle exists

B No cycle exists

C The list is empty

D The pointers are at the head

Meeting of slow and fast pointers inside the list confirms a cycle.

How do you find the start of the cycle after detection?

A Restart the algorithm

B Move fast pointer two steps until it reaches null

C Move slow pointer two steps until it reaches null

D Reset one pointer to head, move both one step until they meet

Resetting one pointer to head and moving both one step at a time finds the cycle start.

Which data structure is Floyd's Cycle Detection Algorithm used on?

A Linked List

B Array

C Stack

D Queue

Floyd's Algorithm is specifically designed to detect cycles in linked lists.

Explain how Floyd's Cycle Detection Algorithm works step-by-step.

Think about how the pointers move and meet inside the list.

Describe how to find the starting node of a cycle after detecting it with Floyd's Algorithm.

Focus on pointer movement after cycle detection.