在二维数组中插入列到指定位置。

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英文:

Insert column in desired location of 2D array

问题

我想选择数组中的一列，比如第2列。我希望将这一列插入到二维数组的特定位置，比如第4列。

例如：

  1. 1 3 5 5 2
  2. 2 4 6 2 1
  3. 3 6 9 1 1

期望的输出将是：

  1. 1 5 5 3 2
  2. 2 6 2 4 1
  3. 3 9 1 6 1

我知道我可以使用以下代码循环，直到逐个交换每一列，直到列在所需位置为止：

  1. for (int[] array1 : array) {
  2.     int temp = array1[col1];
  3.     array1[col1] = array1[col2];
  4.     array1[col2] = temp;
  5. }

然而，如果我使用宽度为30列的大矩阵，这将非常低效。是否有一种方法可以在二维数组中的任何位置插入列，而不必迭代每次交换直到它在正确的位置？

英文:

I'm looking to choose a column of my array, lets say column 2. I want this column to be inserted at a specific location in the 2D array, lets say column 4.

For example:

  1. 1 3 5 5 2
  2. 2 4 6 2 1
  3. 3 6 9 1 1

The desired output would be:

  1. 1 5 5 3 2
  2. 2 6 2 4 1
  3. 3 9 1 6 1

I know I could loop the following code until I 1 by 1 swap every column until the column is in the desired location.

  1. for (int[] array1 : array) {
  2.     int temp = array1[col1];
  3.     array1[col1] = array1[col1];
  4.     array1[col2] = temp;
  5. }

However, if I'm using large matrices such as 30 columns wide, this would be incredibly inefficient. Is there a way to insert the column anywhere in the 2D array without iterating through each swap until it is in the right spot?

答案1

得分: 2

可能通过使用流进行并行处理来提高性能。

应该使用IntStream的行索引来单独处理每一行。

  1.     // 基本的位移方法
  2.     // from, to - 从1开始的索引
  3.     public static void shiftArray(int[] arr, int from, int to) {
  4.         int tmp = arr[from - 1];
  5.         for (int i = from; i < to; i++) {
  6.             arr[i - 1] = arr[i];
  7.         }
  8.         arr[to - 1] = tmp;
  9.     }
  11.     public static void main(String[] args) {
  12. 		int[][] arr2d = {
  13. 		    {1, 3, 5, 5, 2},
  14.             {2, 4, 6, 2, 1},
  15.             {3, 6, 9, 1, 1}
  16. 		};
  17. 		int fromColumn = 2;
  18. 		int toColumn = 4;
  20.         IntStream.range(0, arr2d.length)
  21. 		      .parallel()
  22. 		      .forEach(i -> shiftArray(arr2d[i], fromColumn, toColumn)); // 并行处理每一行
  24.         // 输出位移后的二维数组
  25.         Arrays.stream(arr2d)
  26. 		      .map(Arrays::toString)
  27. 		      .forEach(System.out::println);
  28.     }

输出：

  1. [1, 5, 5, 3, 2]
  2. [2, 6, 2, 4, 1]
  3. [3, 9, 1, 6, 1]
英文:

Possibly, a performance may be improved by using parallel processing with streams.

IntStream of row indexes should be used to handle each row separately.

  1.     // basic shift method
  2.     // from, to - indexes starting from 1
  3.     public static void shiftArray(int[] arr, int from, int to) {
  4.         int tmp = arr[from - 1];
  5.         for (int i = from; i &lt; to; i++) {
  6.             arr[i - 1] = arr[i];
  7.         }
  8.         arr[to - 1] = tmp;
  9.     }
  11.     public static void main(String[] args) {
  12. 		int[][] arr2d = {
  13. 		    {1, 3, 5, 5, 2},
  14.             {2, 4, 6, 2, 1},
  15.             {3, 6, 9, 1, 1}
  16. 		};
  17. 		int fromColumn = 2;
  18. 		int toColumn = 4;
  20.         IntStream.range(0, arr2d.length)
  21. 		      .parallel()
  22. 		      .forEach(i -&gt; shiftArray(arr2d[i], fromColumn, toColumn)); // shift each row in parallel
  24.         // print the 2D array after shift
  25.         Arrays.stream(arr2d)
  26. 		      .map(Arrays::toString)
  27. 		      .forEach(System.out::println);
  28.     }

Output:

  1. [1, 5, 5, 3, 2]
  2. [2, 6, 2, 4, 1]
  3. [3, 9, 1, 6, 1]

答案2

得分: 1

尝试这个。

  1. public static void moveColumn(int[][] matrix, int from, int to) {
  2.     --from; --to;  // 如果列号从零开始，请删除此行。
  3.     int srcPos = from < to ? from + 1 : to;
  4.     int destPos = from < to ? from : to + 1;
  5.     int length = Math.abs(from - to);
  6.     for (int[] array : matrix) {
  7.         int temp = array[from];
  8.         System.arraycopy(array, srcPos, array, destPos, length);
  9.         array[to] = temp;
  10.     }
  11. }

和

  1. int[][] matrix = {
  2.     {1, 3, 5, 5, 2},
  3.     {2, 4, 6, 2, 1},
  4.     {3, 6, 9, 1, 1}
  5. };
  6. moveColumn(matrix, 2, 4);
  7. for (int[] row : matrix)
  8.     System.out.println(Arrays.toString(row));

输出

  1. [1, 5, 5, 3, 2]
  2. [2, 6, 2, 4, 1]
  3. [3, 9, 1, 6, 1]
英文:

Try this.

  1. public static void moveColumn(int[][] matrix, int from, int to) {
  2.     --from; --to;  // If column number begins with zero, remove this line.
  3.     int srcPos = from &lt; to ? from + 1 : to;
  4.     int destPos = from &lt; to ? from : to + 1;
  5.     int length = Math.abs(from - to);
  6.     for (int[] array : matrix) {
  7.         int temp = array[from];
  8.         System.arraycopy(array, srcPos, array, destPos, length);
  9.         array[to] = temp;
  10.     }
  11. }

and

  1. int[][] matrix = {
  2.     {1, 3, 5, 5, 2},
  3.     {2, 4, 6, 2, 1},
  4.     {3, 6, 9, 1, 1}
  5. };
  6. moveColumn(matrix, 2, 4);
  7. for (int[] row : matrix)
  8.     System.out.println(Arrays.toString(row));

output

  1. [1, 5, 5, 3, 2]
  2. [2, 6, 2, 4, 1]
  3. [3, 9, 1, 6, 1]

huangapple
  • 本文由 发表于 2020年7月29日 04:26:09
  • 转载请务必保留本文链接：https://go.coder-hub.com/63142253.html
  • arrays
  • java
  • matrix
  • multidimensional-array
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