java - 如何使用多线程在java中找到二维数组的最大值

Question

我想找到二维数组的最大值。我在没有使用多线程的情况下找到了这个值。如何使用多线程找到二维数组的最大值？我想比较不同方式求数组最大值的速度。

public class Search {

    public int[][] fillMatrix(int matrix[][]) {
        for (int i = 0; i < matrix.length; i++){
            for (int j = 0; j < matrix[i].length; j++){
              matrix[i][j] = (int)(Math.random() * 1000);
            }
        }
        return matrix;
    }

    public int searchMaxValue(int[][] matrix, int row, int column) {
        int max = matrix[0][0];
        for (int a = 0; a < row; a++) {
            for (int b = 0; b < column; b++) {
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (matrix[a][b] > max) {
                    max = matrix[a][b];
                }
            }
        }
        return max;
    }


    public static void main(String[] args) {

        Search search = new Search();
        int[][] matrix = new int[4][100];
        search.fillMatrix(matrix);
        long start = System.currentTimeMillis();
        int max = search.searchMaxValue(matrix, 4, 100);
        long end = System.currentTimeMillis();
        System.out.println("Max value is " + max);
        System.out.println("Time for execution: " + (end - start));
    }
}

Answer 1

下面是您将如何实现它的概述。我没有刻意提供代码，您可以享受自己实现它的乐趣。

create a method to findmax out of an array lets call it findMax(int[]
input)

for each sub array in 2D array (can be accessed using matrix[i])
start a thread to findMax(matrix[i]) (hint: use ExecutorService) in the thread, once max is found, fill it in to ith position of a one dimensional array called results in the thread, indicate its completion(hint: use CountDownLatch)

In the main thread, wait till all threads finish ( hint: use CountDownLatch) Now call findMax(results) and you have the maxiumum from matrix.

注意事项:我们是否需要 fork 与矩阵中的行一样多的线程？那么我们是否使用具有行数的 FixedThreadPool ？