human
Solve in Python:
You are given two images img1 and img2 both of size n x n, represented as binary, square matrices of the same size. (A binary matrix has only 0s and 1s as values.)
We translate one image however we choose (sliding it left, right, up, or down any number of units), and place it on top of the other image.  After, the overlap of this translation is the number of positions that have a 1 in both images.
(Note also that a translation does not include any kind of rotation.)
What is 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 slide img1 to right by 1 unit and down by 1 unit.

The number of positions that have a 1 in both images is 3. (Shown in red)

Example 2:
Input: img1 = [[1]], img2 = [[1]]
Output: 1

Example 3:
Input: img1 = [[0]], img2 = [[0]]
Output: 0

 
Constraints:

n == img1.length
n == img1[i].length
n == img2.length 
n == img2[i].length
1 <= n <= 30
img1[i][j] is 0 or 1.
img2[i][j] is 0 or 1.

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Give me a the largest possible overlap?
assistant
#Here is the largest possible overlap.

class Solution:
    def largestOverlap(self, img1: List[List[int]], img2: List[List[int]]) -> int:
        N = len(img1)
        if N == 1:
            return 1 if img1[0][0] == 1 and img2[0][0] == 1 else 0
        max_slide = N
        sliders = set()
        for i in range(N):
            for j in range(N):
                sliders.add((i, j))
                sliders.add((-i, j))
                sliders.add((i, -j))
                sliders.add((-i, -j))
        
        def slide_and_count(slide):
            res = 0
            left, down = slide
            for i in range(min(N, N-left)):
                i2 = i + left
                for j in range(min(N, N-down)):
                    j2 = j + down
                    if i2 < 0 or j2 < 0:
                        continue
                    try:
                        if img1[i][j] == 1 and img2[i2][j2] == 1:
                            res += 1
                    except:
                        pass
                    
            print(slide, res)
            return res
        
        return max(slide_and_count(slide) for slide in sliders)