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Image Overlap | LEETCODE 835 | Solve In Seconds | Google Microsoft Most Asked Interview

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Image Overlap | LEETCODE 835 | Solve In Seconds | Google Microsoft Most Asked Interview

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Image Overlap is a matrix shifting problem asked at Google and Microsoft interviews — master the best brute force visualization approach to count maximum overlapping ones in seconds with full clarity.

LeetCode Question: https://leetcode.com/problems/image-overlap/
Solution (Java / Python / C++ / C): https://github.com/Shaanworkspace/YOUTUBE-DRIVE/blob/main/Leetcode_Daily/LC_835_Image_Overlap_All_Languages.md
LeetCode 835 Image Overlap asks you to find the maximum number of overlapping ones when one matrix is shifted over another. The brute force approach tries every possible horizontal and vertical shift, counting overlaps at each position — O(n^4) time, O(1) space. This video gives you the best visual explanation of how matrix shifting works, why translation is the key concept, and walks through the complete code with examples. Asked at Google and Microsoft interviews.

00:00 — Best Visualization of How Matrix Shifting Works
This question can be made easy with visualization. I will visualize the problem and solution for you so you understand how things move inside a matrix.

00:36 — Matrix Shifting: How One Grid Moves Over Another
Let us start with the problem. Image overlap means shifting one matrix over another and counting where both have a 1 at the same position.

01:07 — Translation Explained: Why Shifting Is the Key
Translation is the core concept. When you shift img1 by some amount, each cell maps to a new position. We need to find the shift that gives maximum overlap.

02:09 — Visualizing All Possible Shifts Step by Step
A matrix of size n can shift up, down, left, or right. Each shift position is a unique translation. We try every possible shift and count overlapping ones.

04:47 — Counting Overlaps at Each Shift Position
For each shift, iterate through all cells. If img1 has a 1 and the shifted position in img2 also has a 1, increment the count. Track the maximum across all shifts.

07:05 — Example Walkthrough: Counting Overlaps Live
Let us see a concrete example. Walk through the matrix shift by shift, showing exactly which cells overlap and how the count changes at each position.

09:38 — Brute Force Code: Four Nested Loops Explained
The solution uses four nested loops: two for the shift range and two for the matrix cells. For each shift, count overlapping ones. Return the maximum count found.

12:01 — Submit and Verify: All Test Cases Pass
Let us hit submit and see. The brute force approach passes all test cases within the time limit.

13:33 — Complexity Analysis and Subscribe
O(n^4) time, O(1) space. Every shift position checked, every cell compared. Feel free to subscribe and share with friends who need this.

FAQ

Q1: What is LeetCode 835 Image Overlap about?
A1: Given two binary matrices img1 and img2, return the maximum number of ones that overlap when img1 is shifted (translated) in any direction over img2.

Q2: What is the brute force approach for Image Overlap?
A2: Try every possible horizontal and vertical shift of img1 over img2. For each shift, count how many positions have a 1 in both matrices. Return the maximum count.

Q3: What is the time complexity of the brute force solution?
A3: O(n^4) — two loops for the shift range (each up to 2n-1 positions) and two loops for the matrix cells (n x n). For each of the O(n^2) shifts, we check O(n^2) cells.

Q4: Can this problem be solved faster than O(n^4)?
A4: Yes. Using FFT (Fast Fourier Transform) you can solve it in O(n^2 log n) time, but the brute force O(n^4) is simpler and passes within constraints for n up to 30.

Q5: Why is this problem asked at Google and Microsoft?
A5: It tests matrix manipulation, nested loop logic, and the ability to think about shifting/translation — core skills for image processing and grid-based problems.

Q6: What is the space complexity of the brute force approach?
A6: O(1) — no extra data structures needed. We only use a few integer variables for counting and tracking the maximum overlap.

LeetCode #LeetCode835 #ImageOverlap #DSA #Algorithms #Matrix #CodingInterview #ShaanLabs

📺 Watch the full walkthrough on YouTube:

Watch the full Image Overlap | LEETCODE 835 | Solve In Seconds | Google Microsoft Most Asked Interview walkthrough on YouTube

🧠 Want the intuition, not just the code? Join 2,000+ coders getting daily LeetCode breakdowns (Telegram gets them first):

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