MediumNo. 0835
Image Overlap — LeetCode 835 Python Solution
- Pattern
- Matrix and Grid
- Topics
- Array, Matrix
- Reading time
- 2 min
- Source
- leetcode.com
The problem
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.
Example
- 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.
Python solution
class Solution:
def largestOverlap(self, img1: List[List[int]], img2: List[List[int]]) -> int:
n = len(img1)
cnt = Counter()
for i in range(n):
for j in range(n):
if img1[i][j]:
for h in range(n):
for k in range(n):
if img2[h][k]:
cnt[(i - h, j - k)] += 1
return max(cnt.values()) if cnt else 0Complexity
- Time
- O(n4)
- Space · auxiliary
- O(n2)where n is the side length of img1
Pattern: Matrix and Grid
Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 835. Image Overlap is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Matrix.
The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.
Related problems
| No. | Problem | Difficulty |
|---|---|---|
| 0054 | Spiral Matrix | Medium |
| 0059 | Spiral Matrix II | Medium |
| 0289 | Game of Life | Medium |
| 0498 | Diagonal Traverse | Medium |
| 0566 | Reshape the Matrix | Easy |
| 0661 | Image Smoother | Easy |
Frequently asked questions
- How hard is LeetCode 835. Image Overlap?
LeetCode 835. Image Overlap is rated Medium on LeetCode.
- What is the time complexity of LeetCode 835. Image Overlap?
The Python solution on this page runs in O(n4).
- What is the space complexity of LeetCode 835. Image Overlap?
The Python solution on this page uses O(n2), where n is the side length of \textit{img1} auxiliary space.
- What topics does LeetCode 835. Image Overlap cover?
LeetCode 835. Image Overlap is tagged Array and Matrix on LeetCode.