Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 27

Description

Image Overlap

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.

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 == 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.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int largestOverlap(vector<vector<int>>& img1, vector<vector<int>>& img2) {
    int rows = img1.size();
    int cols = img1.front().size();
    vector<int> p1, p2;
    for(int row = 0; row < rows; ++row) {
      for(int col = 0; col < cols; ++col) {
        if(img1[row][col]) {
					// at least double of the cols
          p1.push_back(row * 60 + col);
        }
        if(img2[row][col]) {
          p2.push_back(row * 60 + col);
        }
      }
    }
    unordered_map<int, int> count;
    for(const auto c1 : p1) {
      for(const auto c2 : p2) {
        count[c1 - c2] += 1;
      }
    }
    int answer = 0;
    for(const auto &[_, result] : count) {
      answer = max(answer, result);
    }
    return answer;
  }
};

// Accepted
// 59/59 cases passed (90 ms)
// Your runtime beats 78.47 % of cpp submissions
// Your memory usage beats 34.03 % of cpp submissions (12.3 MB)