Instructions

Test suite

Solution

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

So given a string with embedded newlines like:

9 8 7
5 3 2
6 6 7

representing this matrix:

    1  2  3
  |---------
1 | 9  8  7
2 | 5  3  2
3 | 6  6  7

your code should be able to spit out:

A list of the rows, reading each row left-to-right while moving top-to-bottom across the rows,
A list of the columns, reading each column top-to-bottom while moving from left-to-right.

The rows for our example matrix:

9, 8, 7
5, 3, 2
6, 6, 7

And its columns:

9, 5, 6
8, 3, 6
7, 2, 7

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

$ gradle test

Use gradlew.bat if you're on Windows

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the @Ignore("Remove to run test") annotation.

Source

Warmup to the saddle-points warmup. http://jumpstartlab.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

MatrixTest.java

import org.junit.Ignore;
import org.junit.Test;

import static org.junit.Assert.assertArrayEquals;

public class MatrixTest {

    @Test
    public void extractRowFromOneNumberMatrixTest() {
        String matrixAsString = "1";
        int rowIndex = 1;
        int[] expectedRow = {1};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromMatrixTest() {
        String matrixAsString = "1 2\n3 4";
        int rowIndex = 2;
        int[] expectedRow = {3, 4};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromDiffWidthsMatrixTest() {
        String matrixAsString = "1 2\n10 20";
        int rowIndex = 2;
        int[] expectedRow = {10, 20};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromNonSquareMatrixTest() {
        String matrixAsString = "1 2 3\n4 5 6\n7 8 9\n8 7 6";
        int rowIndex = 4;
        int[] expectedRow = {8, 7, 6};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromOneNumberMatrixTest() {
        String matrixAsString = "1";
        int columnIndex = 1;
        int[] expectedColumn = {1};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnMatrixTest() {
        String matrixAsString = "1 2 3\n4 5 6\n7 8 9";
        int columnIndex = 3;
        int[] expectedColumn = {3, 6, 9};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromNonSquareMatrixTest() {
        String matrixAsString = "1 2 3 4\n5 6 7 8\n9 8 7 6";
        int columnIndex = 4;
        int[] expectedColumn = {4, 8, 6};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromDiffWidthsMatrixTest() {
        String matrixAsString = "89 1903 3\n18 3 1\n9 4 800";
        int columnIndex = 2;
        int[] expectedColumn = {1903, 3, 4};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }
}

class Matrix {

    private int[][] rows;
    private int[][] columns;

    Matrix(String matrixAsString) {
        var lines = matrixAsString.split("\n");
        var rowsCount = lines.length;
        var columnsCount = lines[0].split(" ").length;
        rows = new int[rowsCount][columnsCount];
        columns = new int[columnsCount][rowsCount];
        for (int i = 0; i < rowsCount; i++) {
            var elements = lines[i].split(" ");
            for (int j = 0; j < columnsCount; j++) {
                columns[j][i] = rows[i][j] = Integer.parseInt(elements[j]);
            }
        }
    }

    int[] getRow(int n) {
        return rows[n - 1].clone();
    }

    int[] getColumn(int n) {
        return columns[n - 1].clone();
    }

}

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Artamonov's solution

to Matrix in the Java Track