[Swift]LeetCode1314. 矩阵区域和 | Matrix Block Sum

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Given a m * 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

给你一个 m * n 的矩阵 mat 和一个整数 K ，请你返回一个矩阵 answer ，其中每个 answer[i][j] 是所有满足下述条件的元素 mat[r][c] 的和：

i - K <= r <= i + K, j - K <= c <= j + K
(r, c) 在矩阵内。

示例 1：

输入：mat = [[1,2,3],[4,5,6],[7,8,9]], K = 1
输出：[[12,21,16],[27,45,33],[24,39,28]]
示例 2：

输入：mat = [[1,2,3],[4,5,6],[7,8,9]], K = 2
输出：[[45,45,45],[45,45,45],[45,45,45]]

提示：

m == mat.length
n == mat[i].length
1 <= m, n, K <= 100
1 <= mat[i][j] <= 100