Published at Jul 13 2019
·
0 comments

Instructions

Test suite

Solution

Parse and evaluate simple math word problems returning the answer as an integer.

Problems with no operations simply evaluate to the number given.

What is 5?

Evaluates to 5.

Add two numbers together.

What is 5 plus 13?

Evaluates to 18.

Handle large numbers and negative numbers.

Now, perform the other three operations.

What is 7 minus 5?

2

What is 6 multiplied by 4?

24

What is 25 divided by 5?

5

Handle a set of operations, in sequence.

Since these are verbal word problems, evaluate the expression from
left-to-right, *ignoring the typical order of operations.*

What is 5 plus 13 plus 6?

24

What is 3 plus 2 multiplied by 3?

15 (i.e. not 9)

The parser should reject:

- Unsupported operations ("What is 52 cubed?")
- Non-math questions ("Who is the President of the United States")
- Word problems with invalid syntax ("What is 1 plus plus 2?")

If you'd like, handle exponentials.

What is 2 raised to the 5th power?

32

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.

Inspired by one of the generated questions in the Extreme Startup game. https://github.com/rchatley/extreme_startup

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.Rule;
import org.junit.Test;
import org.junit.Before;
import org.junit.rules.ExpectedException;
import static org.junit.Assert.assertEquals;
public class WordProblemSolverTest {
@Rule
public ExpectedException expectedException = ExpectedException.none();
WordProblemSolver solver;
@Before
public void setup() {
solver = new WordProblemSolver();
}
@Test
public void testJustANumber() {
assertEquals(5, solver.solve("What is 5?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleAddition1() {
assertEquals(2, solver.solve("What is 1 plus 1?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleAddition2() {
assertEquals(55, solver.solve("What is 53 plus 2?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleAdditionWithNegativeNumbers() {
assertEquals(-11, solver.solve("What is -1 plus -10?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleAdditionOfLargeNumbers() {
assertEquals(45801, solver.solve("What is 123 plus 45678?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleSubtraction() {
assertEquals(16, solver.solve("What is 4 minus -12?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleMultiplication() {
assertEquals(-75, solver.solve("What is -3 multiplied by 25?"));
}
@Ignore("Remove to run test")
@Test
public void testSingleDivision() {
assertEquals(-11, solver.solve("What is 33 divided by -3?"));
}
@Ignore("Remove to run test")
@Test
public void testMultipleAdditions() {
assertEquals(3, solver.solve("What is 1 plus 1 plus 1?"));
}
@Ignore("Remove to run test")
@Test
public void testAdditionThenSubtraction() {
assertEquals(8, solver.solve("What is 1 plus 5 minus -2?"));
}
@Ignore("Remove to run test")
@Test
public void testMultipleSubtractions() {
assertEquals(3, solver.solve("What is 20 minus 4 minus 13?"));
}
@Ignore("Remove to run test")
@Test
public void testSubtractionThenAddition() {
assertEquals(14, solver.solve("What is 17 minus 6 plus 3?"));
}
@Ignore("Remove to run test")
@Test
public void testMultipleMultiplications() {
assertEquals(-12, solver.solve("What is 2 multiplied by -2 multiplied by 3?"));
}
@Ignore("Remove to run test")
@Test
public void testAdditionThenMultiplication() {
assertEquals(-8, solver.solve("What is -3 plus 7 multiplied by -2?"));
}
@Ignore("Remove to run test")
@Test
public void testMultipleDivisions() {
assertEquals(2, solver.solve("What is -12 divided by 2 divided by -3?"));
}
@Ignore("Remove to run test")
@Test
public void testUnknownOperation() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is 52 cubed?");
}
@Ignore("Remove to run test")
@Test
public void testNonMathQuestion() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
// See https://en.wikipedia.org/wiki/President_of_the_United_States if you really need to know!
solver.solve("Who is the President of the United States?");
}
@Ignore("Remove to run test")
@Test
public void testMissingAnOperand() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is 1 plus?");
}
@Ignore("Remove to run test")
@Test
public void testNoOperandsOrOperators() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is?");
}
@Ignore("Remove to run test")
@Test
public void testTwoOperationsInARow() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is 1 plus plus 2?");
}
@Ignore("Remove to run test")
@Test
public void testTwoNumbersAfterOperation() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is 1 plus 2 1?");
}
@Ignore("Remove to run test")
@Test
public void testPostfixNotation() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is 1 2 plus?");
}
@Ignore("Remove to run test")
@Test
public void testPrefixNotation() {
expectedException.expect(IllegalArgumentException.class);
expectedException.expectMessage("I'm sorry, I don't understand the question!");
solver.solve("What is plus 1 2?");
}
}
```

```
import java.util.HashMap;
import java.util.Map;
import java.util.function.BinaryOperator;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
class WordProblemSolver {
private static final Pattern EXPRESSION = Pattern.compile(
"^What is (-?\\d+)((?: (?:plus|minus|multiplied by|divided by) -?\\d+)*)\\?$");
private static final Pattern OPERATIONS = Pattern.compile(" (plus|minus|multiplied by|divided by) (-?\\d+)");
private static final Map<String, BinaryOperator<Integer>> OP_IMPLS = new HashMap<String, BinaryOperator<Integer>>() {{
put("plus", Integer::sum);
put("minus", (a, b) -> a - b);
put("multiplied by", (a, b) -> a * b);
put("divided by", (a, b) -> a / b);
}};
int solve(String input) {
Matcher expressionMatcher = EXPRESSION.matcher(input);
if (!expressionMatcher.find()) {
throw new IllegalArgumentException("I'm sorry, I don't understand the question!");
}
int result = Integer.valueOf(expressionMatcher.group(1));
String operations = expressionMatcher.group(2);
if (!operations.isEmpty()) {
Matcher operationMatcher = OPERATIONS.matcher(operations);
while (operationMatcher.find()) {
String operation = operationMatcher.group(1);
int value = Integer.valueOf(operationMatcher.group(2));
result = OP_IMPLS.get(operation).apply(result, value);
}
}
return result;
}
}
```

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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