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calebpollman's solution

to Wordy in the TypeScript Track

Published at Aug 25 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 TypeScript to install the necessary dependencies:

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

Requirements

Install assignment dependencies:

$ yarn install

Making the test suite pass

Execute the tests with:

$ yarn test

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 changing xit to it.

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.

wordy.test.ts

import { WordProblem, ArgumentError } from './wordy'

describe('Word Problem', () => {

  it('add 1', () => {
    const question = 'What is 1 plus 1?'
    expect(new WordProblem(question).answer()).toEqual(2)
  })

  xit('add 2', () => {
    const question = 'What is 53 plus 2?'
    expect(new WordProblem(question).answer()).toEqual(55)
  })

  xit('add negative numbers', () => {
    const question = 'What is -1 plus -10?'
    expect(new WordProblem(question).answer()).toEqual(-11)
  })

  xit('add more digits', () => {
    const question = 'What is 123 plus 45678?'
    expect(new WordProblem(question).answer()).toEqual(45801)
  })

  xit('subtract', () => {
    const question = 'What is 4 minus -12?'
    expect(new WordProblem(question).answer()).toEqual(16)
  })

  xit('multiply', () => {
    const question = 'What is -3 multiplied by 25?'
    expect(new WordProblem(question).answer()).toEqual(-75)
  })

  xit('divide', () => {
    const question = 'What is 33 divided by -3?'
    expect(new WordProblem(question).answer()).toEqual(-11)
  })

  xit('add twice', () => {
    const question = 'What is 1 plus 1 plus 1?'
    expect(new WordProblem(question).answer()).toEqual(3)
  })

  xit('add then subtract', () => {
    const question = 'What is 1 plus 5 minus -2?'
    expect(new WordProblem(question).answer()).toEqual(8)
  })

  xit('subtract twice', () => {
    const question = 'What is 20 minus 4 minus 13?'
    expect(new WordProblem(question).answer()).toEqual(3)
  })

  xit('subtract then add', () => {
    const question = 'What is 17 minus 6 plus 3?'
    expect(new WordProblem(question).answer()).toEqual(14)
  })

  xit('multiply twice', () => {
    const question = 'What is 2 multiplied by -2 multiplied by 3?'
    expect(new WordProblem(question).answer()).toEqual(-12)
  })

  xit('add then multiply', () => {
    const question = 'What is -3 plus 7 multiplied by -2?'
    expect(new WordProblem(question).answer()).toEqual(-8)
  })

  xit('divide twice', () => {
    const question = 'What is -12 divided by 2 divided by -3?'
    expect(new WordProblem(question).answer()).toEqual(2)
  })

  xit('too advanced', () => {
    const question = 'What is 53 cubed?'
    const problem  = new WordProblem(question)

    expect(problem.answer.bind(problem)).toThrowError( ArgumentError )
  })

  xit('irrelevant', () => {
    const question = 'Who is the president of the United States?'
    const problem  = new WordProblem(question)

    expect(problem.answer.bind(problem)).toThrowError( ArgumentError )
  })

})
enum OperationType {
  Divided = 'divided',
  Minus = 'minus',
  Multiplied = 'multiplied',
  Plus = 'plus',
}

type Operation = (initialValue: number, parameter: number) => number;

const operationsKey: { [key: string]: Operation } = Object.freeze({
  [OperationType.Divided]: (initialValue, parameter) => (initialValue /= parameter),
  [OperationType.Minus]: (initialValue, parameter) => (initialValue -= parameter),
  [OperationType.Multiplied]: (initialValue, parameter) => (initialValue *= parameter),
  [OperationType.Plus]: (initialValue, parameter) => (initialValue += parameter),
});

const OPERATIONS = [OperationType.Divided, OperationType.Minus, OperationType.Multiplied, OperationType.Plus];

export class ArgumentError {}

export class WordProblem {
  private operators: string[] = [];
  private parameters: number[] = [];
  private total: number;

  constructor(input: string) {
    const words = input.split(' ');
    words.forEach(word => {
      const parameter = parseInt(word, 10);
      if (parameter) {
        this.parameters.push(parameter);
        return;
      }
      const hasOperator = OPERATIONS.some(operator => operator === word);
      if (hasOperator) {
        this.operators.push(word);
      }
    });

    // initialize total
    this.total = this.parameters.shift() || 0;
  }

  public answer(): number {
    if (!this.operators.length) {
      throw new ArgumentError();
    }
    this.operators.forEach((operator: string, index: number) => {
      const parameter = this.parameters[index];
      const operation = operationsKey[operator];
      this.total = operation(this.total, parameter);
    });
    return this.total;
  }
}

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