We would like to show you a description here but the site won’t allow us. why though ? Can you solve this real interview question? Linked List Cycle - Given head, the head of a linked list, determine if the linked list has a cycle in it. 1) Use slow and fast pointers to find the middle of the linked list. Fast and Slow Pointers is a technique often used in various algorithms and data structures, particularly in linked list operations and cycle detection. Next, make Apr 9, 2024 · In Python programming, particularly when manipulating linked lists or arrays, mastering the “slow and fast pointer” technique can… Jun 18, 2020 · 95% of all singly linked list problems are solved with some type of pointers. Similarly, we can have a fast pointer that walks three steps and a slow pointer that walks one step, if you want to get the 1/3 node. when the fast pointer reaches the end , the slow pointer points to middle node . Slow & Fast Pointer Problems 1. For the problem of detecting cycles in a linked list, there is a universal solution—the fast and slow pointer method (Floyd’s Cycle Detection Algorithm). a very detailed explanation of how we can take any spee Middle of the Linked List - Given the head of a singly linked list, return the middle node of the linked list. 🧠 Key Learnings Today I continued my deep dive into the Fast & Slow Pointer Pattern — and solved a very interesting medium-level problem Circular Array Loop (Problem 457) A question that looks simple at first 🚀 DSA Journey – Day 15 Today, I solved LeetCode Problem 234: Palindrome Linked List using slow and fast pointers 🔹 Problem Given the head of a singly linked list, the task is to determine 🔁 Day 1 of #30DayDSAChallenge Palindrome Linked List – Thinking Beyond Arrays 💡 Continuing my DSA journey with a classic Linked List problem that tests both logic and pointer manipulation Struggling to understand cycle detection in a linked list?This video breaks down LeetCode Problem 141 step by step using the Fast & Slow Pointer (Floyd’s Cyc Apr 6, 2020 · The fast pointer advances the list by n+1 steps from the beginning, while the slow pointer starts from the beginning of the list separating them by n nodes. We have explained Fast and slow pointer technique in Linked List which is also known as tortoise and hare algorithm. 1 day ago · Learn how to detect a cycle in a linked list using the Fast & Slow Pointer technique (Floyd’s Cycle Detection Algorithm) — one of the most important problems for coding interviews. Are you preparing for DSA interviews or trying to master Linked Lists? In this video, I break down the Fast & Slow Pointer technique — one of the most powerf Feb 12, 2024 · But don't quite understand why it works ? ( i. The two pointers will meet at a node. May 25, 2025 · Linked List Series — Basics — Pointer Manipulation Patterns 1. Note that After watching this video, you'll understand slow and fast pointers thoroughly. e slow and fast pointer approach ) when finding middle node in a linked list . The Find the Middle of a Linked List problem is a classic example of how the Slow and Fast Pointer technique simplifies linked list traversal. next? ->Ensures proper splitting ->Avoids infinite General Idea: Every time we move slow pointer once, we move fast pointer twice. Using slow and fast pointers: ->slow moves 1 step ->fast moves 2 steps When fast reaches the end, slow is at the middle. We maintain this constant gap by advancing both pointers together until the fast pointer arrives past the last node. of nodes. Each Node contains a data field and a pointer to the next Node. Jan 10, 2026 · 🚀 Ultimate Linked List Master List for Amazon SDE-1 Prep (Deduplicated & Grouped Logically)Hey LeetCoders! 👋If you're grinding for Amazon SDE-1 (or any FAANG-level role), Linked Lists are a staple in interviews—especially for pointer manipulation, cy Detect Cycle in Linked List 🔁 | Floyd’s Algorithm Explained in 3 Minutes Learn how to detect a cycle in a linked list using the Fast & Slow Pointer technique (Floyd’s Cycle Detection Algorithm) — one of the most important problems for coding interviews. 1) Initialize two pointers, `slow` and `fast`, at the head. Sep 6, 2019 · Fast and slow pointers are often used to navigate a linked list where you don’t know the size in advance. If the linked list has a loop, the `fast` pointer will eventually meet the `slow` pointer. 2) Reverse the second half of the linked list. If there are two middle nodes, return the second middle node. It is used to efficiently solve several problems by using two pointers. If `fast` reaches `null` or `fast. If there’s a cycle, the fast pointer will eventually meet the slow pointer; if not, the fast pointer will reach the end of the list. Unlike traditional linked lists that store data directly in nodes, kernel lists only store next and prev pointers, requiring the use of container_of to recover the containing object. This pattern involves maintaining two pointers that traverse a data structure (like an array or linked list) at different speeds. If the list does not contain a cycle, then the fast pointer will hit the end of the list after n steps for O (n) time, where n is the number of elements in the list. After this card, you will: Understand the structure of singly linked list and doubly linked list; Implement traversal, insertion, deletion in a singly or doubly linked list; Analyze the complexity of different operations in a singly or doubly linked list; Use two-pointer technique (fast-pointer-slow-pointer technique) in the linked list; Solve Dec 11, 2022 · How to use fast and slow pointer technique to solve a pattern of problems of linked list. Jul 11, 2025 · Finding the Start of the Cycle Once the slow and fast pointers meet within the loop, the next step is to identify the start of the cycle. Review key C++ concepts: vectors, strings, I/O, pointers, memory management, linked lists, inheritance, and recursion for exams 1 & 2. Nov 3, 2023 · Similar to two pointers, fast and slow pointers use two pointers to traverse data structures. Here is explained 6 problems related to it. 3) If `slow` and `fast` meet, a cycle exists. 🔍 Core Idea — Split, Sort, and Merge (Linked 3: P-lan Plan the solution with appropriate visualizations and pseudocode. After this card, you will: Understand the structure of singly linked list and doubly linked list; Implement traversal, insertion, deletion in a singly or doubly linked list; Analyze the complexity of different operations in a singly or doubly linked list; Use two-pointer technique (fast-pointer-slow-pointer technique) in the linked list; Solve Fast and Slow Pointers: A Powerful Technique for Solving Linked List Problems In the world of coding interviews and algorithmic problem-solving, linked lists are a common data structure that often appear in various challenges. Perfect for coding interview preparation. Then take one of the two pointers to the head node, the other pointer stay. Mar 1, 2022 · 🔥Hey, guys today we’ll learn about spped of slow and fast pointer in cycle detection in linked list. Apr 12, 2025 · 📘 What is Fast and Slow Pointer? Two pointers are used: Slow Pointer (Tortoise) – moves 1 step at a time Fast Pointer (Hare) – moves 2 steps at a time When both pointers are used on a data structure (like a linked list), their interaction can help detect cycles, find the middle, check for palindromes, and more. The other pointer, the fast pointer, remains at the point where the two pointers initially met. 3) Initialize a variable `max_stability` to keep track of the maximum twin sum. Jan 4, 2025 · The Fast and Slow Pointer technique is a powerful and versatile approach to solve problems involving cycles in linked lists or arrays…. Move `slow` by one step and `fast` by two steps. General Idea: Use the two-pointer technique to detect the cycle and calculate its length. The slow and fast pointers algorithm (also known as Floyd's Cycle Detection algorithm or the Tortoise and Hare algorithm) uses two pointers to determine traits about a graph. While traversing the linked list one of these things will occur- The Fast pointer may reach the end (NULL) which shows that there is no loop in the linked list. It is often used to detect cycles in a linked list. next` is `null`, there is no loop. Conclusion The fast and slow pointers technique is a powerful tool in any programmer’s arsenal, especially when dealing with linked list problems. This technique involves using two pointers that move at different speeds through a data structure. By moving two pointers at different speeds, you can find the middle element in a single pass without extra space. Let us understand:What a circular linked list 📅 Day 10 / 90 – Babua DSA Patterns 2026 🚀 | Fast & Slow Pointers Today’s focus was a single but powerful problem that ties together multiple core ideas of linked lists and pointers: 🔗 🚀 DSA Practice | Palindrome Linked List (Optimal Solution) Today, I solved the Palindrome Linked List problem using an efficient approach with O(n) Time Complexity and O(1) Space Complexity And that’s exactly what this problem is all about: Implementing O (n log n) sorting on a linked list using a fully pointer-based merge sort. The For the problem of detecting cycles in a linked list, there is a universal solution—the fast and slow pointer method (Floyd’s Cycle Detection Algorithm). Steps: Find the middle using fast & slow pointers Reverse the second half of the list Compare both halves node by node This approach avoids extra space and works in linear time. Two Pointers (Slow and Fast Pointer Technique): Use two pointers to find the middle of the list and then compare the two halves. Reversal: Reverse the second half of the list to compare it with the first half. 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. 4) Traverse the first half and the reversed second half of the list: a) Calculate the twin sum for each pair of nodes. How can this be done? Oct 31, 2022 · In the Fast & Slow Pointers technique, two pointers start at the same position and iterate through an array (or linked list) at different speeds. To do this, we reset one of the pointers - let’s say the slow pointer to the head of the linked list. If the fast pointer ever catches up to the slow pointer, there is a loop in the linked list. Learn about the proportional length n and how it determines the movement of the pointers. Step‑3: Move the fast pointer two steps ahead initially. The fast pointer typically moves faster than the slow pointer. Two-Pointer (Slow & Fast) Technique Concept: You have two pointers traveling through the linked list at different speeds. The various elements in a linked list are linked together using pointers. Its ability to solve complex problems with linear time complexity and constant space complexity makes it an invaluable approach in coding interviews and real-world programming scenarios. 2) Move `slow` by one step and `fast` by two steps. Jul 23, 2025 · Move the fast pointer two nodes at a time, while moving the slow pointer one node at a time. 🔹 Why fast = head. In this video, we learn how to check if a linked list is circular using the two pointer (slow & fast) approach. Nov 24, 2023 · Fast and slow pointers are a common pattern used in algorithmic problem-solving, particularly in linked list and two-pointer problems. zero to one: foundational engineering paradigm > concepts -> problem solving: binary search trees, linked list -> techniques: identifying structure, fast and slow pointers > notes > Reorder linked 🌱Day 7/90 – DSA Pattern Challenge Today I stepped into one of the most powerful DSA patterns — Fast & Slow Pointer 🔥 I learned how using two pointers at different speeds helps us solve The slow and fast pointers traverse the list, with fast covering twice the ground. Feb 12, 2024 · Middle Element in Linked List : Fundamental example of fast and slow pointer !! Method 1: Traverse the whole linked list and count the no. Feb 8, 2022 · How can I find a middle element in a linked list by traversing the entire list only once? The length of the list is not given, and I am allowed to only use two pointers. We'll cover examples for even and odd-length linked lists to help you write e Nov 25, 2023 · One elegant solution to this problem is Floyd's slow and fast pointers approach, often likened to two individuals running on a racetrack. Dec 9, 2025 · Master the tortoise and hare algorithm with comprehensive templates, mathematical proofs, and real-world applications. Learn cycle detection, finding middle elements, and advanced techniques. If you've ever wondered how to detect cycles in linked lists, find middle elements without counting, or solve complex problems with surprising efficiency, you're about to discover your new favorite technique. The Fast pointer again catches the slow pointer at some time therefore a loop exists in the Oct 31, 2022 · In the Fast & Slow Pointers technique, two pointers start at the same position and iterate through an array (or linked list) at different speeds. What Are Slow and Fast Pointers? Slow and fast pointers is a technique where two pointers traverse a data structure at different speeds. In this example, we are going to use two pointers to find the mid point of a linked list. 5 days ago · Kernel Linked List Architecture The Linux kernel uses intrusive doubly-linked lists where a struct list_head node is embedded as a member within larger structures. However, both pointers will traverse at most 2n steps in total (including the steps to find the start of the cycle). Once fast pointer reaches the end, the slow pointer is pointing at the middle node. Given two pointers, named slow and fast, both start at the head of the list. 11. 3 days ago · Fast and Slow Pointers is a powerful pattern where you use two pointers and move them at different speeds. Jan 19, 2022 · When using the method of fast and slow, in a linkedlist which has loop. Space Complexity: O(1) because the space used does not scale with the size of the input. Jul 23, 2025 · The faster one is called the fast pointer and the other one is called the slow pointer. Remember that j is the smallest multiple of l greater than s. Internally, pos is used to denote the index of the node that tail's next pointer is connected to. Otherwise, the two pointers will meet after the slow pointer has taken j steps. The pointers can be used to traverse the array or list in either direct, BUT one must move faster than the other. In this tutorial, we're going to do a deep dive on one such algorithm. Dec 11, 2022 · How to use fast and slow pointer technique to solve a pattern of problems of linked list. Step‑2: Initialize two pointers, slow and fast, both pointing to the head of the linked list. In Linked List, unlike arrays, elements are not stored at contiguous memory locations but rather at different memory locations. But this comes with one key difference, the pointers iterate at different speeds. a very detailed explanation of how we can take any spee Aug 13, 2025 · Introduction A linked List is a linear data structure that consists of nodes. Detect a Loop in a Linked List Algorithm: Use two pointers, `slow` and `fast`. Learn the two pointers pattern with step-by-step examples, code templates, and LeetCode practice problems. It can help you solve multiple linked lists and array related problems like: 5 days ago · It uses two pointers moving at different speeds: a "slow" pointer (tortoise) that advances 1 step at a time and a "fast" pointer (hare) that advances 2 steps at a time. This is useful for finding cycles in linked lists. Discover how to solve generic problems using the fast and slow pointer algorithm in linked lists.

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