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.length

• n ==?mat[i].length

• 1 <= m, n, k <= 100

• 1 <= mat[i][j] <= 100

依次遍歷即可，只是沒(méi)想到居然沒(méi)有超時(shí)；

下面是代碼：

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.