It’s been a tough summer: scorching heat, broken air conditioners—and whether full-time SDE roles or NG intern positions, nothing seemed to open. Our business at CSOahelp slowed down… until we discovered that Point72 briefly posted a full-time SDE opening in June 2025. Though it closed almost immediately, one of our students grabbed the chance, got into the interview, and we’re sharing the exact coding question here so you can start prepping for Fall 2025 now.

The Interview Question

Problem:
Given an integer array, remove all zeros in place without allocating extra memory, while preserving the relative order of non-zero elements.

        
def remove_zeros_inplace(array: List[int]) -> None:
    """
    Removes zeros from array.
    Saves ordering of non-zero elements.
    Use O(N) time complexity.
    Uses O(1) additional memory complexity (works inplace).
    """
        
    

One-Pass Fast/Slow-Pointer Solution

1. Initialize slow = 0.
2. Iterate fast from 0 to len(array)-1:
   • If array[fast] != 0, assign array[slow] = array[fast] and increment slow.
3. After the loop, all non-zero elements occupy indices [0..slow-1]. Fill indices [slow..end] with zeros.

        
def remove_zeros_inplace(array: List[int]) -> None:
    slow = 0
    for fast in range(len(array)):
        if array[fast] != 0:
            array[slow] = array[fast]
            slow += 1
    while slow < len(array):
        array[slow] = 0
        slow += 1
        
    

• Time Complexity: O(N) — single pass.
• Space Complexity: O(1) — in-place.

Interviewer Follow-Ups

Our student was asked three times to justify:

1. Time & space complexity
2. Why this two-pointer approach
3. How to minimize unnecessary writes

Thanks to targeted coaching from CSOahelp Interview Assistance, he answered each confidently, passed that round with flying colors, and laid the groundwork to secure his offer.

Ready for Your Next Big Interview?

If you’re preparing for SDE roles at Point72, Meta, TikTok, or other top tech firms—and need to master problem breakdown and edge-case handling—add WeChat csvohelp now. You’ll receive our North America Interview Playbook and can book a free one-on-one mock interview.

CSOahelp | Code Writing | Interview OA Assistance | Interview Representation | Assignment & Lab Writing | Exam Support
A one-stop platform for CS international students:

• Academic Services: online course hosting, thesis help, assignment assistance, exam support
• Career Services: interview coaching, resume polishing
• Privacy guaranteed, pay in installments by project, full refund if unsatisfied

Contact Us:
Email: ceo@csoahelp.com | WeChat: csvohelp