Question

可能重复：
  Which of these two for loops is more efficient in terms of time and cache performance
  Why does the order of the loops affect performance when iterating over a 2D array?

我想知道通过数组的最快方法，在大数组中我正在使用它的重要数据。例如我有：

ushort[, , ,] map = new ushort[3000, 3000, 3, 3]; // [pointX, pointY, stack, lvl]

          for (int i = 0; i < 3000; i++)
              for (int j = 0; j < 3000; j++)
                  for (int k = 0; k < 3; k++)
                      for (int l = 0; l < 3; l++)
                         map[i, j, k, l] = 45001;

它可能是相关的，因为它取决于这些值如何存储在内存中。因此，在这种情况下，最好按此顺序执行此操作 - i-＆gt; j-> k-> l或l-> k-> j-＆gt; i？

另外，它与其他语言不同吗？

Answer 1

它在如何在java中初始化数组的方式上有很大的不同，以下是纯java代码来显示差异，你可以参考下面的代码来提高效率：

public class MutipleArray {

    public static void main(String[] args) {
        long t0 = System.currentTimeMillis();
        int [][][][] map = new int[3000][3000][3][3];
        for (int i = 0; i < 3000; i++)
            for (int j = 0; j < 3000; j++)
                for (int k = 0; k < 3; k++)
                    for (int l = 0; l < 3; l++)
                       map[i][j][k][l] = 45001;
        long t1 = System.currentTimeMillis();
        System.out.println("Time for initializing the first Array:"+(t1-t0)+"ms");

        int [][][][] map2 = new int[3][3][3000][3000];
        for (int i = 0; i < 3; i++)
            for (int j = 0; j < 3; j++)
                for (int k = 0; k < 3000; k++)
                    for (int l = 0; l < 3000; l++)
                        map2[i][j][k][l] = 45001;
        long t2 = System.currentTimeMillis();
        System.out.println("Time for initializing the second Array:"+(t2-t1)+"ms");
    }
}

结果：

Time for initializing the first Array:13570ms
Time for initializing the second Array:495ms

因此，我建议您在java中使用int [] [] [] [] map = new int [3] [3] [3000] [3000]。

效率最高的是通过阵列

1 个答案: