Mine Sweeper 扫雷

生成一个高度h，宽度w，总共m颗雷的矩阵。要求m颗雷随机分布。

参见 @Random subset of size K http://m.it610.com/article/3096698.htm

public int[][] putBomb(int h, int w, int count){
    Random r = new Random();
    int[] bombLocs = new int[count]; // bomb location array
    for (int i = 0; i < count; i++)
        bombLocs[i] = i;
    for (int i = count; i < h * w; i++) {
        int j = r.nextInt(i + 1);
        if (j < count)    bombLocs[j] = i;
    }
    int[][] res = new int[h][w];
    for (int i = 0; i < bombLocs.length; i++) {
        int x = bombLocs[i] / w;
        int y = bombLocs[i] % w;
        res[x][y] = 1;
    }
    return res;
}