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If LinkedList Has Cycle

Certification: Basic Level Accuracy: 71.43% Submissions: 7 Points: 5

Write a Java program to determine if a linked list has a cycle in it. A cycle occurs when a node in a linked list points to a previous node, creating a loop. Return true if there is a cycle in the linked list, otherwise return false.

Example 1
    

  • Input: head = [3,2,0,-4], pos = 1
    • 

  • Output: true
    • 

  • Explanation:

      

    • Tail node connects to the node at index 1 → cycle exists
      • 

    

    •
Example 2
    

  • Input: head = [1,2], pos = 0
    • 

  • Output: true
    • 

  • Explanation:

      

    • Tail node connects to the node at index 0 → cycle exists
      • 

    

    •
Constraints
    

  • 0 ≤ number of nodes ≤ 10^4
    • 

  • -10^5 ≤ Node.val ≤ 10^5
    • 

  • Time Complexity: O(n)
    • 

  • Space Complexity: O(1)
    •
Linked ListEYPhillips
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Hint
Solution

Solution Hints

    
  
  • Use Floyd's Cycle-Finding Algorithm (Tortoise and Hare).
    • 
  
  • Use two pointers moving at different speeds.
    • 
  
  • If there's a cycle, the fast pointer will eventually meet the slow pointer.
    • 
  
  • If there's no cycle, the fast pointer will reach the end of the list.
    •

Steps to solve by this approach:

 Step 1: Check if the list is empty or has only one node (no cycle possible).

 Step 2: Initialize two pointers, slow and fast, both starting at the head.

 Step 3: Move the slow pointer one step at a time and the fast pointer two steps at a time.

 Step 4: If there's a cycle, the fast pointer will eventually catch up to the slow pointer.

 Step 5: If the fast pointer reaches the end of the list (null), then there's no cycle.

 Step 6: Return true if the pointers meet, false otherwise.

Submitted Code :