La transposition d'une matrice à partir d'un tableau 2D

C'est une méthode simple qui retourne un int[][] de la transposée de la matrice...

public static int[][] transposeMatrix(int[][] matrix){
int m = matrix.length;
int n = matrix[0].length;
int[][] transposedMatrix = new int[n][m];
for(int x = 0; x < n; x++) {
for(int y = 0; y < m; y++) {
transposedMatrix[x][y] = matrix[y][x];
}
}
return transposedMatrix;
}

Que d'imprimer une matrice 2D, vous pouvez utiliser une méthode comme ceci:

public static String matrixToString(int[][] a){
int m = a.length;
int n = a[0].length;
String tmp = "";
for(int y = 0; y<m; y++){
for(int x = 0; x<n; x++){
tmp = tmp + a[y][x] + " ";
}
tmp = tmp + "\n";
}
return tmp;
}

OriginalL'auteur thebesttony

Vous pouvez utiliser la sous classe il a la plupart des méthodes que vous souhaitez.

/**
* Class representing square matrix of given size.
* It has methods to rotate by 90, 180 and 270
* And also to transpose and flip on either axis.
* 
* I have used both space efficient methods in transpose and flip
* And simple but more space usage for rotation. 
* 
* This is using builder pattern hence, you can keep on applying
* methods say rotate90().rotate90() to get 180 turn.
* 
*/
public class Matrix {
private int[][] matrix;
final int size;
public Matrix(final int size) {
this.size = size;
matrix = new int[size][size];
for (int i=0;i<size;i++)
for (int j=0;j<size;j++)
matrix[i][j] = i*size + j;
}
public Matrix rotate90() {
int[][] temp = new int[size][size];
for (int i=0;i<size;i++)
for (int j=0;j<size;j++)
temp[i][j] = matrix[size-1-j][i];
matrix = temp;
return this;
}
public Matrix rotate180() {
int[][] temp = new int[size][size];
for (int i=0;i<size;i++)
for (int j=0;j<size;j++)
temp[i][j] = matrix[size-1-i][size-1-j];
matrix = temp;
return this;
}
public Matrix rotate270() {
int[][] temp = new int[size][size];
for (int i=0;i<size;i++)
for (int j=0;j<size;j++)
temp[i][j] = matrix[j][size-1-i];
matrix = temp;
return this;
}
public Matrix transpose() {
for (int i=0; i<size-1; i++) {
for (int j=i+1; j<size; j++) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = tmp;
}
}
return this;
}
public Matrix flipVertical() {
for (int i=0; i<size; i++) {
for (int j=0; j<size/2; j++) {
int tmp = matrix[i][size-1-j];
matrix[i][size-1-j] = matrix[i][j];
matrix[i][j] = tmp;
}
}
return this;
}
public Matrix flipHorizontal() {
for (int i=0; i<size/2; i++) {
for (int j=0; j<size; j++) {
int tmp = matrix[size-1-i][j];
matrix[size-1-i][j] = matrix[i][j];
matrix[i][j] = tmp;
}
}
return this;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
for (int i=0;i<size;i++) {
for (int j=0;j<size;j++) {
sb.append("|");
sb.append(matrix[i][j]);
if (size > 3) {
sb.append("\t");
}
}
sb.append("|\n");
}
return sb.toString();
}
public static void main(String... args) {
Matrix m = new Matrix(3);
System.out.println(m);
//transpose and flipHorizontal is 270 turn (-90)
System.out.println(m.transpose());
System.out.println(m.flipHorizontal());
//rotate 90 further to bring it back to original position
System.out.println(m.rotate90());
//transpose and flip Vertical is 90 degree turn
System.out.println(m.transpose().flipVertical());
}
}

De sortie:

|0|1|2|
|3|4|5|
|6|7|8|
|0|3|6|
|1|4|7|
|2|5|8|
|2|5|8|
|1|4|7|
|0|3|6|
|0|1|2|
|3|4|5|
|6|7|8|
|6|3|0|
|7|4|1|
|8|5|2|

OriginalL'auteur Vineet Abbi