![]() If they don't intersect, then there is no cycle. ![]() The idea behind the algorithm is that, if you have two pointers in a linked list, one moving twice as fast (the hare) than the other (the tortoise), then if they intersect, there is a cycle in the linked list. I came across Floyd's Cycle Detection Algorithm, also known as Floyd's Tortoise and Hare Algorithm. If a node has already been seen, then you know it's a cycle. One of which is to have a hash or set, keeping track of every node seen. This problem can be solved in a couple of different ways. If pos is -1, then there is no cycle in the linked list.įor example, if the input were given that head = and pos = 1, the linked list would look like this: To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail connects to. ![]() Given a linked list, determine if it has a cycle in it. Today's algorithm is about cycles in a linked list: 3 Finding the Only Single Number in an Array 4 Finding the Middle of a Linked List 5 Backspace String Comparisons: Two Ways To Approach a Common Algorithm 6 The Stock Span Problem: Using Stacks To Keep Track Of What's Been Seen 7 Finding the Kth Smallest Element: Walking Through How To Use Depth First Search on a Binary Search Tree 8 The Boyer-Moore Majority Vote Algorithm: Finding the Majority Element in an Array 9 Sorting Characters in a String By Their Frequency 10 Finding the Intersection of Two Arrays 11 Finding the Minimum Path Sum in a Grid with Dynamic Programming 12 Floyd's Tortoise and Hare Algorithm: Finding a Cycle in a Linked List 13 The Sieve of Eratosthenes: Counting the Number of Primes 14 Add Two Numbers Problems: How to Sum Two Linked Lists 15 The Longest Substring With No Repeating Characters 16 Merging Sorted Lists, Two Ways 17 Finding the Longest Common Prefix 18 Reversing a String in Place 19 The ZigZag Conversion Problem 20 The Longest Palindromic Substring: Solving the Problem Using Constant Space 21 Removing an Element in an Array In-Place 22 Solving the Best Time to Buy and Sell Stocks Problem in One Pass 23 Don't Underestimate the Two Pointers: Removing the N-th Node from the End of a Linked List 24 Not an "Easy" Algorithm: Rotating an Array, Three Ways 25 Sudoku Part I: Is the Board Valid? 26 Searching an Array, Two Ways 27 The Climbing Staircase Problem: How to Solve It, and Why the Fibonacci Numbers are Relevant 28 Transposing and Reversing: How to Rotate a 2D Matrix 90 Degrees 29 Turning 38 into 2: How to Solve the Add Digits Problem 30 The Gauss Sum, and Solving for the Missing Number 31 Is this Number the Sum of Two Square Integers? Solving The Sum of Squares Algorithm Two Ways 32 The Word Pattern Algorithm: How to Test if a String Follows a Pattern 33 Finding the Intersection of Two Arrays 34 Top Interview Question: Finding the First Unique Character in a String using Linear Time 35 Solving Pascal's Triangle in JavaScript 36 The Maximum Number of Events Problem 37 Solving Binary Tree Algorithms Using Recursion and Queues 38 From "hello world" to "world hello": Reversing the Words in a String 39 Finding the Most Frequent Elements in an Array 40 Finding the Angle Between the Hands of a Clock 41 The Container with the Most Water: Solving an Algorithm about Areas 1 The Happy Number Problem 2 Kadane's Algorithm & The Maximum Subarray Problem.
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