MatrixDeterminant.java

package com.thealgorithms.matrix;

// Problem: Determinant of a Matrix
// Description: Calculate the determinant of any square matrix using recursion.
// URL: https://en.wikipedia.org/wiki/Determinant

public final class MatrixDeterminant {

    private MatrixDeterminant() {
        // Prevent instantiation
    }

    public static double determinant(double[][] m) {
        int n = m.length;
        for (double[] row : m) {
            if (row.length != n) {
                throw new IllegalArgumentException("Matrix must be square");
            }
        }

        if (n == 1) {
            return m[0][0];
        }

        if (n == 2) {
            return m[0][0] * m[1][1] - m[0][1] * m[1][0];
        }

        double det = 0;
        for (int c = 0; c < n; c++) {
            det += Math.pow(-1, c) * m[0][c] * determinant(minor(m, 0, c));
        }
        return det;
    }

    private static double[][] minor(double[][] m, int row, int col) {
        int n = m.length;
        double[][] min = new double[n - 1][n - 1];
        int r = 0;

        for (int i = 0; i < n; i++) {
            if (i == row) {
                continue;
            }
            int c = 0;
            for (int j = 0; j < n; j++) {
                if (j == col) {
                    continue;
                }
                min[r][c++] = m[i][j];
            }
            r++;
        }
        return min;
    }
}