### Approach To effectively answer the question, "How would you merge two sorted linked lists into one sorted linked list?", follow this structured framework: 1. **Understand the Problem**: Familiarize yourself with the properties of linked lists and the concept of merging. 2. **Identify Inputs and Outputs**: - Inputs: Two sorted linked lists. - Output: A single sorted linked list. 3. **Choose a Method**: Decide on an iterative or recursive approach based on your comfort and the problem constraints. 4. **Outline Your Solution**: Break down the steps needed to implement the chosen method. 5. **Consider Edge Cases**: Think about scenarios such as empty lists, lists of different lengths, and duplicate values. 6. **Explain Complexity**: Discuss the time and space complexity of your solution. ### Key Points - **Clarity**: Ensure your explanation is clear and step-by-step to demonstrate your thought process. - **Efficiency**: Highlight the efficiency of your solution in terms of time (O(n + m)) and space (O(1) for iterative). - **Edge Cases**: Be prepared to discuss how your solution handles edge cases, as this demonstrates thoroughness. - **Coding Skills**: Interviewers are looking for both your reasoning and coding skills, so be ready to code on a whiteboard or in an online editor. ### Standard Response To merge two sorted linked lists into one sorted linked list, I would approach the problem as follows: 1. **Initialization**: - Create a dummy node that will help simplify the merging process. - Use a pointer to track the current position in the new list. 2. **Iterate through Both Lists**: - Compare the current nodes of both lists. - Append the smaller node to the new list and move the pointer in the merged list and the corresponding list forward. 3. **Handle Remaining Nodes**: - Once one list is completely traversed, append the remaining nodes of the other list to the merged list. 4. **Return the Merged List**: - The merged list can be accessed starting from the next node of the dummy node. Here’s a sample implementation in Python: ```python class ListNode: def __init__(self, val=0, next=None): self.val = val self.next = next def mergeTwoLists(l1: ListNode, l2: ListNode) -> ListNode: dummy = ListNode(0) current = dummy while l1 and l2: if l1.val < l2.val: current.next = l1 l1 = l1.next else: current.next = l2 l2 = l2.next current = current.next current.next = l1 if l1 else l2 return dummy.next ``` This code effectively merges two sorted linked lists by iterating through both lists and maintaining the order. The use of a dummy node simplifies edge cases and the final return ensures the correct new list is returned. ### Tips & Variations #### Common Mistakes to Avoid - **Not Handling Edge Cases**: Forgetting to check for empty lists can lead to null pointer exceptions. - **Inefficient Solutions**: Using excessive space or time complexity unnecessarily complicates the solution. - **Poor Explanation**: Failing to articulate your thought process can lead to misinterpretation of your coding abilities. #### Alternative Ways to Answer - **Recursive Approach**: Explain how a recursive method can also be used to merge linked lists by defining a base case and recursively merging the lists. Example (Recursive): ```python def mergeTwoLists(l1: ListNode, l2: ListNode) -> ListNode: if not l1: return l2 if not l2: return l1 if l1.val < l2.val: l1.next = mergeTwoLists(l1.next, l2) return l1 else: l2.next = mergeTwoLists(l1, l2.next) return l2 ``` #### Role-Specific Variations - **Technical Roles**: Focus on time and space complexities in detail, and discuss edge cases thoroughly. - **Managerial Roles**: Emphasize teamwork and collaboration in problem-solving, discussing how you would communicate the solution to a team. - **Creative Roles**: Highlight innovative approaches or algorithms you might consider for merging data structures creatively. ### Follow-Up Questions - **Can you explain the time and space complexity of your solution?** - **How would you modify the solution if the lists were not sorted?** - **What would you do if the linked lists contained cycles?** - **How would your approach change if you were required to merge multiple lists instead of just two?** This