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How to Solve Linked List Cycle Problem
Master the Linked List Cycle LeetCode problem with undetectable real-time assistance. Get instant solutions and explanations during your coding interviews.
Phantom Code generates complete solutions and debugging hints that you can use while explaining your approach, so you stay calm and in control.
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Start Free for WindowsEasy#141
LeetCode ProblemLinked List Cycle
Given head, the head of a linked list, determine if the linked list has a cycle in it. There is a cycle 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 is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise, return false. Example 1: Example 2: Example 3: Constraints: Follow up: Can you solve it using O(1) (i.e. constant) memory?
Hash TableLinked ListTwo Pointers
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Problem Breakdown
Understanding the Linked List Cycle Problem
Let's break down this LeetCode problem and understand what makes it challenging in interview settings.
Problem Statement
Given head, the head of a linked list, determine if the linked list has a cycle in it. There is a cycle 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 is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise, return false. Example 1: Example 2: Example 3: Constraints: Follow up: Can you solve it using O(1) (i.e. constant) memory?
EasyProblem #141
LeetCodeLinked List Cycle
Related Topics
Hash TableLinked ListTwo Pointers
How Phantom Code Helps
Get real-time assistance for Linked List Cycle problems during coding interviews. Phantom Code provides instant solutions and explanations.
Examples
# Example 1
Input
head = [3,2,0,-4], pos = 1
Output
true
# Example 2
Input
head = [1,2], pos = 0
Output
true
# Example 3
Input
head = [1], pos = -1
Output
false
Constraints
The number of the nodes in the list is in the range [0, 104].
-105 <= Node.val <= 105
pos is -1 or a valid index in the linked-list.
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Solve Linked List Cycle — Given head, the head of a linked list, determine if the linked list has a cycle ...
Here's the optimal approach using Hash Table:
def solve(input):
# Optimal O(n) solution
return result
Time: O(n) | Space: O(n)
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Undetectability Checklist
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Zoom
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Google Meet
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HackerRank
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CodeSignal
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CoderPad
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We work with Zoom, HackerRank, CodeSignal, CoderPad and other web-based platforms. Check the compatibility note and request a browser link if a specific desktop app is unsupported.
Frequently Asked Questions
Common questions about solving Linked List Cycle and using Phantom Code during coding interviews.
How does Phantom Code help me solve coding problems like Linked List Cycle during interviews?
Phantom Code generates complete solutions instantly with proper complexity analysis, letting you focus on explaining your approach and demonstrating problem-solving skills rather than getting stuck on implementation details during high-pressure situations.
What if the interviewer asks follow-up questions or modifications to problems like Linked List Cycle?
Phantom Code adapts in real-time. Screenshot the modified problem or use audio mode to capture the interviewer's follow-up, and get an updated solution within seconds — including edge cases and optimizations.
Can Phantom Code help me communicate my solution for problems like Linked List Cycle?
Yes. Phantom Code provides step-by-step approach explanations with 3 progressive thoughts, so you can walk through your solution naturally. It also provides time and space complexity analysis to discuss trade-offs.
How does Phantom Code assist with different programming languages for Linked List Cycle type problems?
Phantom Code supports 11 programming languages including Python, Java, C++, JavaScript, TypeScript, Go, Rust, Ruby, Swift, Kotlin, and C#. Set your preferred language and get idiomatic solutions.
What coding mistakes does Phantom Code help me avoid during Linked List Cycle interviews?
Phantom Code catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
Is Phantom Code detectable when solving problems like Linked List Cycle during live interviews?
No. Phantom Code runs as an invisible desktop overlay that doesn't appear in screen shares, recordings, or proctoring software. It works with Zoom, HackerRank, CodeSignal, CoderPad, and all major platforms.
How does Phantom Code help when I'm struggling with Linked List Cycle style questions under pressure?
The AI provides structured guidance: first the approach (what algorithm/data structure to use and why), then the implementation with clean code, and finally complexity analysis. This helps you think clearly even under pressure.
Does Phantom Code work for the coding platforms used in Linked List Cycle interviews?
Yes. Phantom Code works with all major coding platforms including LeetCode, HackerRank, CodeSignal, CoderPad, HackerEarth, and any browser-based coding environment.
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