Matrix Block Sum LeetCode solution in Java

1
class Solution {
2
  public int[][] matrixBlockSum(int[][] mat, int k) {
3
    int m = mat.length, n = mat[0].length;
4
    int[][] answer = new int[m][n];
5
    for (int i = 0; i < m; i++) {
6
      for (int j = 0; j < n; j++) {
7
        int val = 0;
8
        // take new variables to get starting index of mat[r][c]
9
        int p = i - k, q = j - k;
10
        // make sure p and q are atleast 0 (i.e. valid)
11
        while (p < 0) p++;
12
        while (q < 0) q++;
13
        // traverse again in the matrix with starting at p,q and ending at i+k and j+k
14
        // add conditions to make sure the indices dont cross the values of m and n
15
        for (int x = p; x <= i + k && x < m; x++) {
16
          for (int y = q; y <= j + k && y < n; y++) {
17
            val += mat[x][y];
18
          }
19
        }
20
        answer[i][j] = val;
21
      }
22
    }
23
    return answer;
24
  }
25
}