Java/src/main/java/com/thealgorithms/maths/MatrixUtil.java

package com.thealgorithms.maths;

import java.math.BigDecimal;
import java.util.Arrays;
import java.util.Objects;
import java.util.Optional;
import java.util.function.BiFunction;
import java.util.stream.IntStream;

/**
 * @author: caos321
 * @date: 31 October 2021 (Sunday)
 */
public class MatrixUtil {

    public static boolean isValid(final BigDecimal[][] matrix) {
        return matrix != null && matrix.length > 0 && matrix[0].length > 0;
    }

    public static boolean hasEqualSizes(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return (isValid(matrix1) && isValid(matrix2) && matrix1.length == matrix2.length && matrix1[0].length == matrix2[0].length);
    }

    public static boolean canMultiply(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return (isValid(matrix1) && isValid(matrix2) && matrix1[0].length == matrix2.length);
    }

    public static Optional<BigDecimal[][]> operate(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2, final BiFunction<BigDecimal, BigDecimal, BigDecimal> operation) {
        if (!hasEqualSizes(matrix1, matrix2)) {
            return Optional.empty();
        }

        final int rowSize = matrix1.length;
        final int columnSize = matrix1[0].length;

        final BigDecimal[][] result = new BigDecimal[rowSize][columnSize];

        IntStream.range(0, rowSize).forEach(rowIndex -> IntStream.range(0, columnSize).forEach(columnIndex -> {
            final BigDecimal value1 = matrix1[rowIndex][columnIndex];
            final BigDecimal value2 = matrix2[rowIndex][columnIndex];

            result[rowIndex][columnIndex] = operation.apply(value1, value2);
        }));

        return Optional.of(result);
    }

    public static Optional<BigDecimal[][]> add(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return operate(matrix1, matrix2, BigDecimal::add);
    }

    public static Optional<BigDecimal[][]> subtract(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        return operate(matrix1, matrix2, BigDecimal::subtract);
    }

    public static Optional<BigDecimal[][]> multiply(final BigDecimal[][] matrix1, final BigDecimal[][] matrix2) {
        if (!canMultiply(matrix1, matrix2)) {
            return Optional.empty();
        }

        final int size = matrix1[0].length;

        final int matrix1RowSize = matrix1.length;
        final int matrix2ColumnSize = matrix2[0].length;

        final BigDecimal[][] result = new BigDecimal[matrix1RowSize][matrix2ColumnSize];

        IntStream.range(0, matrix1RowSize)
            .forEach(rowIndex
                -> IntStream.range(0, matrix2ColumnSize)
                       .forEach(columnIndex
                           -> result[rowIndex][columnIndex] = IntStream.range(0, size)
                                                                  .mapToObj(index -> {
                                                                      final BigDecimal value1 = matrix1[rowIndex][index];
                                                                      final BigDecimal value2 = matrix2[index][columnIndex];

                                                                      return value1.multiply(value2);
                                                                  })
                                                                  .reduce(BigDecimal.ZERO, BigDecimal::add)));

        return Optional.of(result);
    }

    public static void assertThat(final BigDecimal[][] actual, final BigDecimal[][] expected) {
        if (!Objects.deepEquals(actual, expected)) {
            throw new AssertionError(String.format("expected=%s but was actual=%s", Arrays.deepToString(expected), Arrays.deepToString(actual)));
        }
    }

    public static void main(final String[] args) {
        {
            final BigDecimal[][] matrix1 = {
                {new BigDecimal(3), new BigDecimal(2)},
                {new BigDecimal(0), new BigDecimal(1)},
            };

            final BigDecimal[][] matrix2 = {
                {new BigDecimal(1), new BigDecimal(3)},
                {new BigDecimal(2), new BigDecimal(0)},
            };

            final BigDecimal[][] actual = add(matrix1, matrix2).orElseThrow(() -> new AssertionError("Could not compute matrix!"));

            final BigDecimal[][] expected = {
                {new BigDecimal(4), new BigDecimal(5)},
                {new BigDecimal(2), new BigDecimal(1)},
            };

            assertThat(actual, expected);
        }

        {
            final BigDecimal[][] matrix1 = {
                {new BigDecimal(1), new BigDecimal(4)},
                {new BigDecimal(5), new BigDecimal(6)},
            };

            final BigDecimal[][] matrix2 = {
                {new BigDecimal(2), new BigDecimal(0)},
                {new BigDecimal(-2), new BigDecimal(-3)},
            };

            final BigDecimal[][] actual = subtract(matrix1, matrix2).orElseThrow(() -> new AssertionError("Could not compute matrix!"));

            final BigDecimal[][] expected = {
                {new BigDecimal(-1), new BigDecimal(4)},
                {new BigDecimal(7), new BigDecimal(9)},
            };

            assertThat(actual, expected);
        }

        {
            final BigDecimal[][] matrix1 = {
                {new BigDecimal(1), new BigDecimal(2), new BigDecimal(3)},
                {new BigDecimal(4), new BigDecimal(5), new BigDecimal(6)},
                {new BigDecimal(7), new BigDecimal(8), new BigDecimal(9)},
            };

            final BigDecimal[][] matrix2 = {
                {new BigDecimal(1), new BigDecimal(2)},
                {new BigDecimal(3), new BigDecimal(4)},
                {new BigDecimal(5), new BigDecimal(6)},
            };

            final BigDecimal[][] actual = multiply(matrix1, matrix2).orElseThrow(() -> new AssertionError("Could not compute matrix!"));

            final BigDecimal[][] expected = {
                {new BigDecimal(22), new BigDecimal(28)},
                {new BigDecimal(49), new BigDecimal(64)},
                {new BigDecimal(76), new BigDecimal(100)},
            };

            assertThat(actual, expected);
        }
    }
}