如何交换二维数组的行和列？

Question

我正在尝试为 'transpose' 二维整数数组编写一个方法，其中交换原始矩阵的行和列。

但是，我不知道如何实现这一点。这个方法怎么写出来？

public class Matrix {
    private int[][] numbers;

    public Matrix(int rows, int colums) {
        if (rows < 1)
            rows = 1;
        else
            rows = rows;
        if (colums < 1)
            colums = 1;
        else
            colums = colums;
        numbers = new int[rows][colums];
    }

    public final void setNumbers(int[][] numbers) {
        this.numbers = numbers;
    }

    public int[][] getNumbers() {
        return numbers;
    }

    public int[][] transpose() {
        int[][] transpose = getNumbers();
        return numbers;
    }
}

Answer 1

您可以遍历行和列并将每个元素 [i,j] 分配给转置后的 [j,i]:

/**
 * Transposses a matrix.
 * Assumption: mat is a non-empty matrix. i.e.:
 * 1. mat != null
 * 2. mat.length > 0
 * 3. For every i, mat[i].length are equal and mat[i].length > 0
 */
public static int[][] transpose(int[][] mat) {
    int[][] result = new int[mat[0].length][mat.length];
    for (int i = 0; i < mat.length; ++i) {
        for (int j = 0; j < mat[0].length; ++j) {
            result[j][i] = mat[i][j];
        }
    }
    return result;
}

Answer 2

矩阵的转置

int m = 4;
int n = 5;

// original matrix
int[][] arr1 = {
        {11, 12, 13, 14, 15},
        {16, 17, 18, 19, 20},
        {21, 22, 23, 24, 25},
        {26, 27, 28, 29, 30}};

// transposed matrix
int[][] arr2 = new int[n][m];

// swap rows and columns
IntStream.range(0, n).forEach(i ->
        IntStream.range(0, m).forEach(j ->
                arr2[i][j] = arr1[j][i]));

// output to the markdown table
String matrices = Stream.of(arr1, arr2)
        .map(arr -> Arrays.stream(arr).map(Arrays::toString)
                .collect(Collectors.joining("<br>")))
        .collect(Collectors.joining("</pre> | <pre>"));

System.out.println("| original matrix | transposed matrix |");
System.out.println("|---|---|");
System.out.println("| <pre>" + matrices + "</pre> |");

original matrix	transposed matrix
[11, 12, 13, 14, 15] [16, 17, 18, 19, 20] [21, 22, 23, 24, 25] [26, 27, 28, 29, 30]	[11, 16, 21, 26] [12, 17, 22, 27] [13, 18, 23, 28] [14, 19, 24, 29] [15, 20, 25, 30]

^{另请参阅：}

如何交换二维数组的行和列？

How to swap rows and columns of a 2d array?

java

arrays

transpose

matrix

multidimensional-array

矩阵的转置