Cramer.java

import java.util.Scanner;

public class Cramer {
	
	Double [][]A;
	Double []B;
	int size;
	
	public Cramer() {
		A = null;
		B = null;
		size = 0;
	}
	
	public Cramer (Double[][] m2, Double[] x) {
		this.A = m2;
		this.B = x;
		this.size = x.length;
	}
	
	public Double[] solve () {
		Double [][]tempMatrix = new Double[size][size];
		Double []x = new Double[3];
		
		Double detCohef = this.calculateCoeficientsMatrixDeterminant();
		
		for (int i=0;i<size;i++) {
			for (int k=0;k<size;k++) {
				for (int l=0;l<size;l++) {
					tempMatrix[k][l] = A[k][l];						
				}
			}
			for (int k=0;k<size;k++) {
				tempMatrix[k][i] = B[k];
			}
			Double det = this.calculateDeterminant(tempMatrix, size);
			x[i] = det/detCohef;
		}
		return x;
	}
	
	public Double calculateCoeficientsMatrixDeterminant() {
		return calculateDeterminant(this.A, this.size);
	}
	
	public Double calculateDeterminant (Double [][]m, int sizeM ) {
		if ( sizeM == 1 ) {
			return m[0][0];
		} 
		else if ( sizeM == 2 ) {
			// You should save a lot of recursive calls by calculating
			// a 2x2 determinant here
			return m[0][0] * m[1][1] - m[0][1] * m[1][0];
		} 
		else {
			Double sum = 0.0;
			int multiplier = -1;
			for (int i=0; i<sizeM;i++) {
				multiplier = multiplier == -1 ? 1 : -1;
				Double [][]nM = this.copyMatrix(m, sizeM, i);
				Double det = multiplier * m[0][i] * calculateDeterminant(nM, sizeM-1);
				sum += det;
			}
			return sum;
		}
	}
	
	public Double[][] copyMatrix (Double [][]m, int size, int col) {
		int sizeM = size -1;
		Double [][]result = new Double[sizeM][sizeM];
		int nI = 0;
		for (int i=1; i<size;i++) {
			int nJ = 0;
			for (int j=0; j<size;j++) {
				if ( j != col) {
					result[nI][nJ] = m[i][j];
					nJ++;
				}
			}
			nI++;
		}
		return result;
	}
	
}