Watch 10 video solutions for Matrix Block Sum, a medium level problem involving Array, Matrix, Prefix Sum. This walkthrough by NeetCode has 192,989 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
Given a m x n matrix mat and an integer k, return a matrix answer where each answer[i][j] is the sum of all elements mat[r][c] for:
i - k <= r <= i + k,j - k <= c <= j + k, and(r, c) is a valid position in the matrix.
Example 1:
Input: mat = [[1,2,3],[4,5,6],[7,8,9]], k = 1 Output: [[12,21,16],[27,45,33],[24,39,28]]
Example 2:
Input: mat = [[1,2,3],[4,5,6],[7,8,9]], k = 2 Output: [[45,45,45],[45,45,45],[45,45,45]]
Constraints:
m == mat.lengthn == mat[i].length1 <= m, n, k <= 1001 <= mat[i][j] <= 100