Zad3.java

import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Zad3 {
	public static void main(String[] args) {
		System.out.print("Podaj rozmiar: ");
		int n;

		Random random = new Random(System.nanoTime());

		try (Scanner scanner = new Scanner(System.in)) {
			n = scanner.nextInt();
		}

		double[][] matrix = createMatrix(n, random);
		System.out.println(Arrays.stream(matrix).map(Arrays::toString).collect(Collectors.joining("\n")));
		double[][] inverse = inverse(matrix);
		System.out.println("Inverse");
		System.out.println(Arrays.stream(inverse).map(Arrays::toString).collect(Collectors.joining("\n")));
	}

	private static double[][] createMatrix(int n, Random random) {
		double[][] result = new double[n][n];

		for (int y = 0; y < result.length; y++) {
			for (int x = 0; x < result[y].length; x++) {
				result[y][x] = random.nextDouble() * 10;
			}
		}

		return result;
	}

	private static double[][] inverse(double[][] matrix) {
		double[][] inverse;

		double[][] attached = new double[matrix.length][matrix.length];
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix.length; j++) {
				double[][] temp = new double[matrix.length - 1][matrix.length - 1];
				int a = 0, b = 0;
				for (int w = 0; w < matrix.length; w++) {
					for (int z = 0; z < matrix.length; z++) {
						if (w != i && z != j) {
							if (b >= temp.length) {
								b = 0;
								a++;
							}
							temp[a][b] = matrix[w][z];
							b++;
						}
					}
				}

				double det = det(temp);

				if ((i + j) % 2 != 0) {
					if (det > 0) {
						det -= 2 * det;
					} else {
						det -= 2 * det;
					}
				}
				attached[i][j] = det;
			}
		}
		attached = transpose(attached);
		inverse = multiply(1 / det(matrix), attached);
		return inverse;
	}

	private static double[][] multiply(double n, double[][] matrix) {
		double[][] result = new double[matrix.length][matrix[0].length];
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[0].length; j++) {
				result[i][j] = (matrix[i][j] * n);
			}
		}
		return result;
	}

	private static double[][] transpose(double[][] matrix) {
		double[][] result = new double[matrix[0].length][matrix.length];
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[0].length; j++) {
				result[j][i] = matrix[i][j];
			}
		}
		return result;
	}

	private static double det(double[][] matrix) {
		double det = 0;

		double[][] newMatrix = new double[matrix.length + (matrix.length - 1)][matrix[0].length];

		for (int i = 0, _i = 0; i < newMatrix.length; i++, _i++) {
			for (int j = 0; j < matrix[0].length; j++) {
				if (_i < matrix.length) {
					newMatrix[i][j] = matrix[_i][j];
				} else {
					_i = 0;
					newMatrix[i][j] = matrix[_i][j];
				}
			}
		}

		double product = 1;
		int _i;

		for (int i = 0; i < matrix.length; i++) {
			_i = i;
			for (int j = 0; j < matrix[0].length; j++) {
				product *= newMatrix[_i][j];
				_i++;
			}
			det += product;
			product = 1;
		}

		product = 1;
		for (int i = 0; i < matrix.length; i++) {
			_i = i;
			for (int j = matrix[0].length - 1; j >= 0; j--) {
				product *= newMatrix[_i][j];
				_i++;
			}
			det -= product;
			product = 1;
		}

		return det;
	}
}