0835. Image Overlap

https://leetcode.com/problems/image-overlap

Description

You are given two images, img1 and img2, represented as binary, square matrices of size n x n. A binary matrix has only 0s and 1s as values.

We translate one image however we choose by sliding all the 1 bits left, right, up, and/or down any number of units. We then place it on top of the other image. We can then calculate the overlap by counting the number of positions that have a 1 in both images.

Note also that a translation does not include any kind of rotation. Any 1 bits that are translated outside of the matrix borders are erased.

Return the largest possible overlap.

Example 1:

**Input:** img1 = [[1,1,0],[0,1,0],[0,1,0]], img2 = [[0,0,0],[0,1,1],[0,0,1]]
**Output:** 3
**Explanation:** We translate img1 to right by 1 unit and down by 1 unit.
![](https://assets.leetcode.com/uploads/2020/09/09/overlap_step1.jpg)
The number of positions that have a 1 in both images is 3 (shown in red).
![](https://assets.leetcode.com/uploads/2020/09/09/overlap_step2.jpg)

Example 2:

**Input:** img1 = [[1]], img2 = [[1]]
**Output:** 1

Example 3:

**Input:** img1 = [[0]], img2 = [[0]]
**Output:** 0

Constraints:

• n == img1.length == img1[i].length

• n == img2.length == img2[i].length

• 1 <= n <= 30

• img1[i][j] is either 0 or 1.

• img2[i][j] is either 0 or 1.

ac