矩阵区域和

// Java Stream solution
// This solution involves similar logic to the previous one but attempts to leverage Java Streams for more compact code. However, Java Streams are not ideal for multi-dimensional array operations. The code uses nested loops with a focus on functional-style operations.

import java.util.stream.IntStream;

public int[][] matrixBlockSumStream(int[][] mat, int k) {
    int m = mat.length;
    int n = mat[0].length;
    int[][] answer = new int[m][n];

    IntStream.range(0, m).forEach(i -> {
        IntStream.range(0, n).forEach(j -> {
            answer[i][j] = IntStream.rangeClosed(Math.max(0, i - k), Math.min(m - 1, i + k))
                .flatMap(r -> IntStream.rangeClosed(Math.max(0, j - k), Math.min(n - 1, j + k))
                    .map(c -> mat[r][c]))
                .sum();
        });
    });

    return answer;
}