What is your strategy for programming a linked list to reverse its order?

Question Analysis

The question is asking about your approach or strategy for reversing a linked list. This is a common problem in coding interviews that tests your understanding of linked list data structures and your ability to manipulate pointers. You need to demonstrate your knowledge of how linked lists work, and how to alter the order of their nodes. The typical linked list can either be singly or doubly linked, so consider clarifying which type you're dealing with if not specified. The solution usually involves iterating through the list and reversing the direction of the pointers.

Answer

To reverse a singly linked list, you can use an iterative approach. Here's a step-by-step strategy:

1. Initialize three pointers:

   • prev as NULL
   • current as the head of the linked list
   • next as NULL

2. Iterate through the linked list:

   • While current is not NULL, repeat the following steps:
     • Store the next node: next = current->next
     • Reverse the current node's pointer: current->next = prev
     • Move the prev and current pointers one step forward:
       • prev = current
       • current = next

3. Update the head:

   • Once the loop is finished, prev will be pointing at the new head of the reversed list. Thus, update the head: head = prev

This algorithm works in O(n) time complexity and O(1) space complexity as it iteratively reverses the links between nodes without using extra space for a new list.

Here's a simple code implementation in C++:

struct Node {
    int data;
    Node* next;
};

Node* reverseLinkedList(Node* head) {
    Node* prev = NULL;
    Node* current = head;
    Node* next = NULL;
    
    while (current != NULL) {
        next = current->next;  // Store the next node
        current->next = prev;  // Reverse the current node's pointer
        prev = current;        // Move prev one step forward
        current = next;        // Move current one step forward
    }
    
    head = prev;  // Update the head to the new front of the list
    return head;
}

This approach effectively reverses the linked list in place, utilizing the minimum necessary resources.