Published at Nov 17 2019
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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

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

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

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.

Warmup to the `saddle-points`

warmup. http://jumpstartlab.com

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

```
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));
}
}
```

```
import java.util.ArrayList;
import java.util.Arrays;
class Matrix {
public int[][] matrix;
Matrix(String matrixAsString) {
String[] rows = matrixAsString.split("\n");
matrix = new int[rows.length][];
for (int i = 0; i < matrix.length; i++) {
matrix[i] = Arrays.stream(rows[i].split(" ")).mapToInt(Integer::parseInt).toArray();
}
}
int[] getRow(int rowNumber) {
// Had to add this line since it seems the matrix tests were changed to start from 1 not 0.
rowNumber--;
return matrix[rowNumber];
}
int[] getColumn(int columnNumber) {
// Had to add this line since it seems the matrix tests were changed to start from 1 not 0.
columnNumber--;
int[] columnArray = new int[matrix.length];
for (int i = 0; i < columnArray.length; i++) {
columnArray[i] = matrix[i][columnNumber];
}
return columnArray;
}
}
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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