LeetCode 21 – Merge Two Sorted Lists [C Solution] | Linked Lists in C

LeetCode 21 – Merge Two Sorted Lists [C Solution] | Linked Lists in C Welcome to *CodeWithBK* — your complete learning hub for mastering C programming concepts. 🔎 What You'll Learn in this video: Problem: Combine two sorted linked lists (l1 and l2) into a single sorted list, reusing their existing nodes. Algorithm Outline: - Check if either list is empty—if so, return the other list immediately. - Determine which initial node will be the head of the merged list. - Use two pointers (curr1, curr2) to iterate through l1 and l2, and a pointer tail that always tracks the last node of the merged list. - Compare values, link the smaller node to tail's next, advance the corresponding source pointer and tail. - When one list runs out, append the rest of the other list. - Return the head pointer. (No dummy node allocations required.) This method achieves O(m + n) time and O(1) additional space, fully in‑place using only existing nodes 🧠 Concepts Covered: Linked list basics, pointer manipulation, iterative solution ✅ Why This Approach? - Cleaner Memory Usage: No dummy node means no extra (even temporary) nodes. - Simplified Control Flow: Initialization establishes a proper head, removing post‑loop pointer juggling. - Efficient & In-Place: Only existing nodes are touched, maintaining O(1) aux space and linear time. 🧠 Perfect for: - C programming learners - Coding interview preparation - Practicing linked list manipulation 📚 Related Videos: - LeetCode 92 C Solution – Reverse Linked List II : https://youtu.be/-9lFJC-ZlF0 - LeetCode 707 C Solution – Design a Linked List : https://youtu.be/k_Xj-jc0QWc - LeetCode 19 C Solution – Remove Nth Node From End of List : https://youtu.be/IvYUJd3NR_g 👨‍💻 Timestamps: 00:00 – Introduction 00:44 – Problem description 01:47 – algorithm and solution 08:02 – C Code implementation 14:54 – testing the code 👍 Don't forget to like, comment, and subscribe for more tutorials on C programming, LeetCode solutions and other coding topics! Stay connected: Subscribe: https://www.youtube.com/@CodeWithBK Email: [email protected] Discord: https://discord.gg/3d2U25Zs Instagram ▶️ https://www.instagram.com/balkrishna_srivastava Coding mentor profile: https://www.codementor.io/@balkrishnasrivastava12 For 1:1 sessions, reach out to me here : https://www.codementor.io/@balkrishnasrivastava12 My YouTube channel where I teach in Hindi : https://www.youtube.com/@CodeWithBKHindi #CProgramming #CodeWithBK #LinkedList #DataStructures #LeetCode #CForBeginners #PointersInC #LearnCProgramming #CPrograms #LeetCodeSolution