String Calculator

A simple string calculator that can add numbers from a given string input with customizable delimiters and validation options.

Implementation Approach

The calculator is implemented using two classes:

1. Calculator

• Handles basic addition logic.
• Ensures numbers larger than the allowed maximum are ignored.
• Throws errors for negative numbers if required.

2. StringCalculator (Extends Calculator)

• Parses input strings and extracts numbers.
• Supports custom delimiters, multi-character delimiters, and multiple delimiters.
• Converts input into a format suitable for Calculator to process.

Test-Driven Development (TDD) Approach

I followed the TDD methodology by first writing failing test cases before implementing the functionality. Each feature is built incrementally, ensuring all tests passed before moving to the next. I have completed all the steps of TDD Kata 1.

Usage

const calculator = new StringCalculator();
const result = calculator.add("1,2,3"); // Returns 6
console.log(result); // 6

Features

1. Supports adding numbers from a comma-separated string

calculator.add("1,2"); // Returns 3

2. Handles empty string and single-digit string

calculator.add(""); // Returns 0
calculator.add("5"); // Returns 5

3. Handles an unknown amount of numbers

calculator.add("1,2,3,4,5"); // Returns 15

4. Supports newline (\n) as a delimiter

calculator.add("1\n2,3"); // Returns 6

5. Allows custom delimiters

You can define a custom delimiter by specifying it at the beginning of the string using the pattern: //[delimiter]\n[numbers…]

calculator.add("//;\n1;2"); // Returns 3

6. Throws an exception for negative numbers

calculator.add("1,-2,3"); // Throws "negative numbers not allowed -2"
calculator.add("-1,-2,-3"); // Throws "negative numbers not allowed -1,-2,-3"

7. Ignores numbers greater than a specified limit (default: 1000)

calculator.add("2,1001"); // Returns 2 (1001 is ignored)

8. Supports multiple custom delimiters, including delimiters of any length

calculator.add("//[***]\n1***2***3"); // Returns 6
calculator.add("//[*][%]\n1*2%3"); // Returns 6
calculator.add("//[***][%%]\n1***2%%3"); // Returns 6

Customizable Options

1. Allow Only Positive Numbers

By default, negative numbers are not allowed. If a negative number is found, an error will be thrown.

calculator.add("-9"); // Throws "negative numbers not allowed -9"
calculator.add("1,2,-3"); // Throws "negative numbers not allowed -3"

To allow negative numbers, set allowOnlyPositiveNumbers to false:

calculator.add("1,2,-3", false); // Returns 0 (default sum behavior)

2. Ignore Numbers Larger than a Certain Limit

By default, numbers larger than 1000 are ignored.

calculator.add("1,1001,2"); // Returns 3 (1001 is ignored)
calculator.add("1001"); // Returns 0

You can change this limit by setting maxAllowedNumber:

calculator.add("1,2000,2", true, 2000); // Returns 2003 (2000 is now included)

3. Custom Delimiters

You can define a custom delimiter by specifying it at the beginning of the string in the format: "//[delimiter]\n[numbers…]"

calculator.add("//;\n1;2"); // Returns 3 (using `;` as a delimiter)

4. Multi-character Delimiters

You can use a delimiter of any length.

calculator.add("//[***]\n1***2***3"); // Returns 6

5. Multiple Delimiters

You can define multiple custom delimiters of any length.

calculator.add("//[*][%]\n1*2%3"); // Returns 6
calculator.add("//[***][%%]\n1***2%%3"); // Returns 6