Given a m x nmatrix matand an integer k, return a matrix answerwhere each answer[i][j]is the sum of all elements mat[r][c]for:

(资料图)

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.length

n == mat[i].length

1 <= m, n, k <= 100

1 <= mat[i][j] <= 100

依次遍历即可，只是没想到居然没有超时；

下面是代码：

Runtime: 83 ms, faster than 22.89% of Java online submissions for Matrix Block Sum.

Memory Usage: 44.8 MB, less than 5.07% of Java online submissions for Matrix Block Sum.