How do you partition a linked list around a value x, ensuring that all nodes with values less than x come before nodes with values greater than or equal to x?

How do you partition a linked list around a value x, ensuring that all nodes with values less than x come before nodes with values greater than or equal to x?

How do you partition a linked list around a value x, ensuring that all nodes with values less than x come before nodes with values greater than or equal to x?

Approach

To effectively answer the question "How do you partition a linked list around a value x, ensuring that all nodes with values less than x come before nodes with values greater than or equal to x?", follow this structured framework:

  1. Understand the Problem: Clearly define what is meant by partitioning a linked list.

  2. Identify Input and Output: Specify the input (the linked list and the value x) and the desired output (the rearranged linked list).

  3. Outline the Algorithm: Develop a step-by-step approach to solve the problem.

  4. Consider Edge Cases: Think through possible scenarios, including empty lists or all nodes being less than or greater than x.

  5. Provide Time and Space Complexity: Assess the efficiency of your solution.

Key Points

  • Clarity: Demonstrate a clear understanding of linked lists and the partitioning process.

  • Logical Flow: Make sure your thought process is logical and easy to follow.

  • Efficiency: Highlight the importance of a solution that operates in O(n) time complexity with O(1) space complexity when possible.

  • Technical Terms: Use appropriate terminology (e.g., pointers, nodes, linked lists) to convey professionalism and expertise.

Standard Response

Here’s a structured response to the interview question:

To partition a linked list around a value x, ensuring that all nodes with values less than x come before nodes with values greater than or equal to x, I would follow these steps:

  • Initialize Two New Lists: Create two separate linked lists:

  • less_head: To store nodes with values less than x.

  • greater_head: To store nodes with values greater than or equal to x.

  • Iterate Through the Original List: Traverse the original linked list and for each node:

  • If the node's value is less than x, append it to the less_head list.

  • If the node's value is greater than or equal to x, append it to the greater_head list.

  • Combine the Two Lists: After the traversal, connect the end of the lesshead list to the head of the greaterhead list.

  • Handle Edge Cases: Ensure that if either list is empty, the other list is returned directly.

  • Return the New List: Finally, return the combined list starting from less_head.

Here is a sample implementation in Python:

class ListNode:
 def __init__(self, val=0, next=None):
 self.val = val
 self.next = next

def partition(head: ListNode, x: int) -> ListNode:
 less_head = ListNode(0) # Dummy node for less than x
 greater_head = ListNode(0) # Dummy node for greater than or equal to x
 less = less_head
 greater = greater_head

 current = head
 while current:
 if current.val < x:
 less.next = current
 less = less.next
 else:
 greater.next = current
 greater = greater.next
 current = current.next

 # Connect the two lists
 greater.next = None # Important to avoid cycles
 less.next = greater_head.next # Combine the two lists

 return less_head.next # Return the new head

Tips & Variations

Common Mistakes to Avoid

  • Neglecting Edge Cases: Failing to handle cases where the linked list is empty or where all nodes belong to one partition.

  • Incorrect Pointer Manipulation: Forgetting to set the next pointers correctly can lead to cycles or loss of data.

  • Inefficient Solutions: Using extra space unnecessarily or not achieving linear time complexity.

Alternative Ways to Answer

  • For a technical role, focus on the algorithm's complexity and provide a more in-depth explanation of pointer manipulation.

  • In a managerial interview, emphasize teamwork and how you would approach problem-solving collaboratively.

Role-Specific Variations

  • Technical Positions: Discuss potential optimizations or variations of the algorithm, such as in-place partitioning.

  • Creative Roles: Illustrate how you would visualize the process or use diagrams to explain your thought process.

Follow-Up Questions

  • "How would you modify your approach if the linked list was doubly linked?"

  • "Can you explain how this solution scales with larger datasets?"

  • "What would you do if the partition value x was not provided?"

  • Interviewers may ask follow-up questions to delve deeper, such as:

This structured approach not only conveys your technical understanding but also demonstrates your ability to communicate complex ideas clearly and effectively, which is crucial in any job interview setting

Question Details

Difficulty
Medium
Medium
Type
Coding
Coding
Companies
IBM
Intel
IBM
Intel
Tags
Data Structure
Problem-Solving
Algorithm Design
Data Structure
Problem-Solving
Algorithm Design
Roles
Software Engineer
Data Scientist
Backend Developer
Software Engineer
Data Scientist
Backend Developer

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