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rafael1fcosta's solution

to Wordy in the Java Track

Published at Sep 10 2019 · 0 comments
Instructions
Test suite
Solution

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

Iteration 0 — Numbers

Problems with no operations simply evaluate to the number given.

What is 5?

Evaluates to 5.

Iteration 1 — Addition

Add two numbers together.

What is 5 plus 13?

Evaluates to 18.

Handle large numbers and negative numbers.

Iteration 2 — Subtraction, Multiplication and Division

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

Iteration 3 — Multiple Operations

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)

Iteration 4 — Errors

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?")

Bonus — Exponentials

If you'd like, handle exponentials.

What is 2 raised to the 5th power?

32

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

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

Submitting Incomplete Solutions

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

WordProblemSolverTest.java

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.regex.Matcher;
import java.util.regex.Pattern;

public class WordProblemSolver {

    private final String INPUT_PATTERN = "^What is ([-]+[0-9]+|[0-9]+)( (plus|minus|multiplied by|divided by) ([-]+[0-9]+|[0-9]+))*\\?";
    private final String NUMBER_PATTERN = "[-]*[0-9]+";
    private final String OPERATOR_PATTERN = "(plus|minus|multiplied|divided)";

    private final String EXCEPTION_MESSAGE = "I'm sorry, I don't understand the question!";

    public int solve(String input) {
        if (!input.matches(INPUT_PATTERN)) {
            throw new IllegalArgumentException(EXCEPTION_MESSAGE);
        }

        Matcher numbers = Pattern.compile(NUMBER_PATTERN).matcher(input);
        Matcher operators = Pattern.compile(OPERATOR_PATTERN).matcher(input);

        numbers.find();
        String firstNumber = numbers.group();

        if (!operators.find()) {
            return Integer.valueOf(firstNumber);
        }
        String operator = operators.group();

        numbers.find();
        String secondNumber = numbers.group();

        int result = resolve(firstNumber, operator, secondNumber);

        if (numbers.find()) {
            secondNumber = numbers.group();

            operators.find();
            operator = operators.group();

            result = resolve(String.valueOf(result), operator, secondNumber);
        }

        return result;
    }

    private int resolve(String firstNumber, String operation, String secondNumber) {

        int a = Integer.valueOf(firstNumber);
        int b = Integer.valueOf(secondNumber);

        switch (operation) {
        case "plus":
            return a + b;
        case "minus":
            return a - b;
        case "multiplied":
            return a * b;
        case "divided":
            return a / b;

        default:
            throw new IllegalStateException();
        }
    }
}

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