Poison

Generate Minesweeper Matrix

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class Solution {
    private static final int[][] DIRECTIONS = new int[][]{{0, -1}, {0, 1}, {-1, 0}, {1, 0}, {1, 1}, {-1, -1}, {-1, 1}, {1, -1}};

    public int[][] generateMinesweeperMatrix(int m, int n, int k) {
        int[][] matrix = new int[m][n];

        for (int i = 0; i < k; i++) {
            matrix[i / m][i % n] = -1;
        }
        for (int i = 0; i < m * n; i++) {
            int randomIndex = ThreadLocalRandom.current().nextInt(i, m * n);
            swap(matrix, i, randomIndex);
        }

        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == -1) {
                    continue;
                }

                int count = 0;
                for (int[] direction : DIRECTIONS) {
                    int nextI = i + direction[0];
                    int nextJ = j + direction[1];
                    if (nextI >= 0 && nextI < m && nextJ >= 0 && nextJ < n && matrix[nextI][nextJ] == -1) {
                        count++;
                    }
                }
                matrix[i][j] = count;
            }
        }

        return matrix;
    }
}