Fast And Slow Pointer To Find Duplicates. For the problem of detecting cycles in a linked list, there is a un

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). Sep 15, 2025 · Ever wondered how to detect if a linked list has a cycle without using extra memory? The Fast & Slow Pointers technique, also known as Floyd’s Cycle Detection Algorithm, is your secret weapon Nov 25, 2023 · Just as the racetrack analogy helps visualize the movements of the slow and fast pointers, Floyd's algorithm offers an elegant and efficient solution for finding the middle of a linked list. Oct 23, 2019 · Here is the proof: If the Hare (fast pointer) is one step behind the Tortoise (slow pointer): The fast pointer moves two steps and the slow pointer moves one step, and they both meet. If you don’t know much about Floyd’s Tortoise and Hare algorithm, you can learn more about linked list cycle detection. innoskrit. This is the best place to expand your knowledge and get prepared for your next interview. , "find the start of a cycle"). The point where they meet is the duplicate. google. With fast and slow pointers we can find… We would like to show you a description here but the site won’t allow us. Phase 2: Once a cycle is detected, reset one of the pointers to the beginning of the array and move both pointers one step at a time. Being the slow pointer incremented in steps of one position at at time you know for sure that, in the presence of a cycle, it will pass through the beginning of the cycle. com/watch?v=_ynpEGuYsW4& Sep 15, 2025 · Ever wondered how to detect if a linked list has a cycle without using extra memory? The Fast & Slow Pointers technique, also known as Floyd’s Cycle Detection Algorithm, is your secret weapon Build, ship, and iterate faster with the most popular open source coding agent. Start with two pointers, the slow pointer progresses one step at a time (slow = nums [slow]), and the fast pointer which advances two steps at a time (fast = nums [nums [fast]]). Each time, fast moves two steps, and slow moves one step. You must solve the problem without modifying the array nums and using only constant extra space. 9K subscribers Subscribe Sep 19, 2023 · If the slow and fast pointers are equal, then the duplicate number is the value of the slow pointer. @Louis93 t(m,n) provides all values where the slow and fast pointer meet. Note: This is an excellent problem to learn the fast and slow pointers approach. It is used to efficiently solve several problems by using two pointers. Questions in English: https://docs. We have discussed two O(n) time in-place solutions. Note: You must not modify the array (assume the array is read only). . Note: This is an excellent problem to learn problem-solving using fast and slow pointers in the linked list. Given a singly linked list, write a program to find the middle element of the linked list. Approach : We start by initializing a slow pointer and a fast pointer and then move the fast pointer with 2x the speed of the slow pointer until they both point to the same May 26, 2025 · Their meeting point will be at the start of the cycle — the repeated number. Key Idea 🔹 Use two pointers: A slow pointer (slow) that moves one step at a time. Find The Duplicates in an Array (Floyds cycle) slow and fast pointers (Day -08) CoffeeBites with Vijay 103 subscribers Subscribed Given a sorted array, write a program to remove duplicates from the array. The goal should be to use a single loop and O(1) extra space to find the middle element. You must use only constant, O (1) extra space. Find the Duplicate Number | Day 013 | 5 Ways | Binary Search | Bit Manipulation | Slow & Fast Aryan Mittal 54. Example 1: Input: nums = [1,3,4,2,2] Output Can you solve this real interview question? Find the Duplicate Number - Level up your coding skills and quickly land a job. youtube. Beginner-friendly solution for Leetcode daily challenge problem. Two Pointers Playlist • Two Pointers more Oct 7, 2019 · If they both meet that means there are duplicates in the array. Two Pointers Playlist • Two Pointers more Sep 16, 2025 · In algorithm problems, sometimes we need to detect cycles, find the middle of a list, or track repeated patterns efficiently. The point where the slow and fast pointers meet again will be the duplicate number in the list (in this case, 9). Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Example 1: Input: nums = [1,3,4,2,2] Output Feb 20, 2023 · Learn how to remove duplicates from a sorted array in Java using a two-pointer approach. If there's a loop in the array – indicating a duplicate – the pointers will eventually meet. 2 days ago · Fast-Slow Pointer Pattern: This pattern is fundamental for detecting cycles in circular buffers and finding middle elements without knowing list length (essential when malloc tracking is unavailable). Duplicate detection is a common interview topic, and while brute force or hash-based solutions may work, they’re not always Transmission Control Protocol accepts data from a data stream, divides it into chunks, and adds a TCP header creating a TCP segment. , slow == fast), reset one of the pointers (either slow or fast) to nums[0]. zero to one: foundational engineering paradigm > concepts -> problem solving: binary search trees, linked list -> techniques: identifying structure, fast and slow pointers > notes > Reorder linked 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. Example 1: Input: nums = [1,3,4,2,2] Output 4 days ago · Each item points to a block as shown. The problem needs to detect loops or intersections (e. May 14, 2025 · In this post, we’ll tackle LeetCode 287: Find the Duplicate Number. After detecting the cycle, reset one pointer (slow) to the head of the list. Jan 11, 2025 · Continue this until slow and fast meet. Access Method: To locate a record, we find the index record with the largest key value less than or equal to the search key, and then follow the pointers sequentially. By observing their movement, we can detect loops, locate special The problem involves repeated numbers or sequences (e. com/spreadsheets/d/1QNSEok-WD4LCPTrZlqq5VVTX0NbXQf27WUjkGi3aBu0/edit?usp=sharingQuestions in Mandarin: https://docs Apr 19, 2025 · link Here values in nums is a permutation of the indices. #leetcode Code Link: https://learn. We need to remove repeated elements so that there is a single occurrence of each element and return the length of the array containing unique elements. com/watch?v=_ynpEGuYsW4& Build, ship, and iterate faster with the most popular open source coding agent. , "find the duplicate in an array"). Initialize another pointer, called the second pointer, to the beginning of the array. Sep 20, 2023 · The slow pointer moves one step at a time, while the fast pointer jumps two steps. We need to return the second middle node if the node count is even. e. The first meeting point of these two pointers will be inside the cycle. Example 1: Input: nums = [1,3,4,2,2] Output 287. Assume that there is only one duplicate number, find the duplicate one. This creates a cycle. Find the Duplicate: Once the cycle is detected (i. Efficient solution with code walkthrough and explanation. By moving two pointers at different speeds, you can find the middle element in a single pass without extra space. Jul 23, 2025 · To find the starting node of a cycle in a linked list, follow the steps below: Using above algorithm we can find the meeting point (if cycle exists) where the slow and fast pointers intersect inside the cycle. Given two pointers, named slow and fast, both start at the head of the list. What Are Slow and Fast Pointers? Slow and fast pointers is a technique where two pointers traverse a data structure at different speeds. Can you solve this real interview question? Find the Duplicate Number - Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive. Palindrome Linked List (234) This combined three ideas perfectly: • Fast & Slow pointer → find the middle • Reverse the second half of the linked list • Apply Two Pointer pattern → Day 27 Problem solving on leetcode 1Day = 1 Question on leetcode 👍 👍 🚀 LeetCode 876 | Middle of the Linked List This problem is a classic example of using the fast and slow pointer 🔁 Fast & Slow Pointer Pattern — Revisited Spent some time revisiting the Fast–Slow Pointer (Floyd’s Cycle Detection) pattern today — one of those techniques that quietly shows up in Jan 11, 2025 · Find the Duplicate: Once the cycle is detected (i. Now, place the fast pointer back to the first element (2) and move both the slow and fast pointers one step at a time. 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. This can be an array, singly-linked list, or a graph. Duplicate detection is a common interview topic, and while brute force or hash-based solutions may work, they’re not always Nov 25, 2023 · Just as the racetrack analogy helps visualize the movements of the slow and fast pointers, Floyd's algorithm offers an elegant and efficient solution for finding the middle of a linked list. In this way, we can find the duplicate element in the array. A fast pointer (fast) that moves two steps at a time. g. If the Hare (fast pointer) is two steps behind the Tortoise (slow pointer): The fast pointer moves two steps and the slow pointer moves one step. [16] The term TCP packet appears in both informal and formal usage, whereas in more precise terminology segment refers to the TCP protocol data unit (PDU Aug 6, 2024 · The fast and slow pointer (also known as the tortoise and hare approach) is quite a famous two-pointer technique used to determine properties about directed data structures: an array, a single-linked list, or a graph all be used. Initialize slow =0; Then move slow and fast pointer as one jump; till the time they both collide. Approach : We start by initializing a slow pointer and a fast pointer and then move the fast pointer with 2x the speed of the slow pointer until they both point to the same May 4, 2023 · If we now update both the pointers, one at a time, this means that the slow pointer will travel a distance of (D X) (D − X) and the fast pointer will also travel a distance of D X D −X to meet the slow pointer at the start of the cycle. The Fast & Slow Pointer technique solves these problems smartly by using two pointers moving at different speeds: Slow pointer: moves one step at a time. Following are the steps involved in finding the duplicate number using the linked list cycle: Beginner-friendly solution for Leetcode daily challenge problem. Locate the Entry Point: Move both pointers one step at a time until Jan 30, 2021 · That's when I discovered fast and slow pointers and it has now opened up a whole world of possibilities. Keep the other pointer (fast) at the meeting point. Dummy Node Technique: The dummy node pattern simplifies edge case handling in embedded systems where null pointer checks are critical. Example 1: Input: nums = [1,3,4,2,2] Output After a few steps, the slow and fast pointers will meet at an index (in this case, at 7). Jan 8, 2024 · In a cycle, the distance traveled by the fast pointer is twice that of the slow pointer. The above problem can be solved by the cycle finding algorithm in Linked List using two pointers slow and fast, the slow pointer moves by one step and fast move by two steps in every iteration. Fast and Slow Pointer The fast and slow pointer technique (also known as the tortoise and hare algorithm) uses two pointers to determine traits about directional data structures. C++ Implementation Java Implementation We have explained Fast and slow pointer technique in Linked List which is also known as tortoise and hare algorithm. If fast reaches the end, it means there is no cycle. in/blog/find-the-duplicate-number/Start of Loop in the Linked List: https://www. Example 1: Input: nums = [1,3,4,2,2] Output Intuition : We use the linked list by using the technique to find cycle in the list. The TCP segment is then encapsulated into an Internet Protocol (IP) datagram, and exchanged with peers. We would like to show you a description here but the site won’t allow us. There is only one repeated number in nums, return this repeated number. If we consider i and nums [i] as consecutive nodes of a linked list, we have a permutation of the indices in the linked list. Say nums [i] = 2 and nums [j] = 2. Feb 12, 2024 · Fast and Slow Pointer Similar to the two pointers pattern, the fast and slow pointers pattern uses two pointers to traverse an iterable data structure at different speeds. The element to which both the pointers meet will be the element repeated in the list. Dec 2, 2024 · Steps: Phase 1: Use two pointers, a slow pointer (tortoise) and a fast pointer (hare), to detect the cycle in the array. To locate a record, we find the index record with the largest search key value less than or equal to the search key value we are looking for. Fast pointer: moves two steps (or more) at a time. Example 1: Input: nums = [1,3,4,2,2] Output Can you solve this real interview question? Find the Duplicate Number - Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

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