Data Structures and Algorithms: Reorder List 🎯

Welcome to this comprehensive guide on the Reorder List problem, a classic example of linked lists manipulation and algorithms. Let's dive in! 💡

Understanding the Problem

Given a singly linked list l1 and a singly linked list l2, both of which are sorted in ascending order, merge them into a single sorted list by alternating the nodes.

Example:

l1 = [1, 3, 5]
l2 = [2, 4, 6]

Merged list: [1, 2, 3, 4, 5, 6]

Approach

We'll create a new list that will store the merged nodes, iterate over both lists, and insert the nodes alternately.

Algorithm

Initialize two pointers, p1 and p2, at the head of the first and second lists respectively.
Create a new list merged.
Continue until both lists are empty.
Add the node pointed by p1 or p2 to the merged list.
Move the pointer to the next node.
Return the merged list.

Python Implementation

Here's a Python implementation of the above algorithm.

python

def merge_lists(l1, l2):
    merged = []
    p1, p2 = l1, l2

    while p1 and p2:
        merged.append(p1.val)
        merged.append(p2.val)
        p1 = p1.next if p1.next else None
        p2 = p2.next if p2.next else None

    merged += p1 or []
    merged += p2 or []

    return merged

📝 Note: This code handles the case when one of the lists is empty, by appending the remaining nodes from the non-empty list to the merged list.

Quiz

That's it for this lesson on the Reorder List problem! Now you know how to merge two sorted linked lists by alternating their nodes. ✅

Stay tuned for more in-depth explanations and practical examples on Data Structures and Algorithms at CodeYourCraft!