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Reverse LinkedList

Certification: Basic Level Accuracy: 83.33% Submissions: 6 Points: 5

Write a Java program to reverse a singly linked list. Return the head of the reversed list.

Example 1
    

  • Input: head = [1,2,3,4,5]
    • 

  • Output: [5,4,3,2,1]
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  • Explanation:

      

    • Reverse each link → end becomes new head
      • 

    

    •
Example 2
    

  • Input: head = [1,2]
    • 

  • Output: [2,1]
    •
Constraints
    

  • 0 ≤ nodes ≤ 5000
    • 

  • -5000 ≤ Node.val ≤ 5000
    • 

  • Time Complexity: O(n)
    • 

  • Space Complexity: O(1)
    •
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Hint
Solution

Solution Hints

    
  
  • Use the iterative approach with three pointers: prev, current, and next.
    • 
  
  • Maintain these pointers to reverse the links between nodes.
    • 
  
  • Start with prev as null and current as head.
    • 
  
  • For each node, store the next node, reverse the link, and update pointers.
    • 
  
  • Return prev as the new head after the traversal.
    •

Steps to solve by this approach:

 Step 1: Initialize three pointers: prev = null, current = head, and next = null.

 Step 2: Iterate through the linked list until current becomes null.

 Step 3: Inside the loop, first store the next node: next = current.next.

 Step 4: Reverse the current node's pointer: current.next = prev.

 Step 5: Move prev and current one step forward: prev = current and current = next.

 Step 6: After the loop ends, prev will be pointing to the new head of the reversed list.

 Step 7: Return prev as the new head of the reversed linked list.

Submitted Code :