exercism/csharp/international-calling-connoisseur

International Calling Connoisseur

Welcome to International Calling Connoisseur on Exercism's C# Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

A dictionary is a collection of elements where each element comprises a key and value such that if a key is passed to a method of the dictionary its associated value is returned. It has the same role as maps or associative arrays do in other languages.

A dictionary can be created as follows:

new Dictionary<int, string>();
// Empty dictionary

Or

new Dictionary<int, string>
{
    [1] = "One",
    [2] = "Two"
};

// Or

new Dictionary<int, string>
{
    {1, "One"},
    {2, "Two"}
};
// 1 => "One", 2 => "Two"

Note that the key and value types are part of the definition of the dictionary.

Once constructed, entries can be added or removed from a dictionary using its built-in methods Add and Remove.

Retrieving or updating values in a dictionary is done by indexing into the dictionary using a key:

var numbers = new Dictionary<int, string>
{
   {1, "One"},
   {2, "Two"}
};

// Set the value of the element with key 2 to "Deux"
numbers[2] = "Deux";

// Get the value of the element with key 2
numbers[2];
// => "Deux"

You can test if a value exists in the dictionary with:

var dict = new Dictionary<string, string>{/*...*/};
dict.ContainsKey("some key that exists");
// => true

Enumerating over a dictionary will enumerate over its key/value pairs. Dictionaries also have properties that allow enumerating over its keys or values.

Instructions

In this exercise you'll be writing code to keep track of international dialling codes via an international dialing code dictionary.

The dictionary uses an integer for its keys (the dialing code) and a string (country name) for its values.

You have 9 tasks which involve the DialingCodes static class.

1. Create a new dictionary

Implement the (static) method DialingCodes.GetEmptyDictionary() that returns an empty dictionary.

DialingCodes.GetEmptyDictionary();
// => empty dictionary

2. Create a pre-populated dictionary

There exists a pre-populated dictionary which contains the following 3 dialing codes: "United States of America" which has a code of 1, "Brazil" which has a code of 55 and "India" which has a code of 91. Implement the (static) DialingCodes.GetExistingDictionary() method to return the pre-populated dictionary:

DialingCodes.GetExistingDictionary();
// => 1 => "United States of America", 55 => "Brazil", 91 => "India"

3. Add a country to an empty dictionary

Implement the (static) method DialingCodes.AddCountryToEmptyDictionary() that creates a dictionary and adds a dialing code and associated country name to it.

DialingCodes.AddCountryToEmptyDictionary(44, "United Kingdom");
// => 44 => "United Kingdom"

4. Add a country to an existing dictionary

Implement the (static) method DialingCodes.AddCountryToExistingDictionary() that adds a dialing code and associated country name to a non-empty dictionary.

DialingCodes.AddCountryToExistingDictionary(DialingCodes.GetExistingDictionary(),
  44, "United Kingdom");
// => 1 => "United States of America", 44 => "United Kingdom", 55 => "Brazil", 91 => "India"

5. Get the country name matching a dialing code

Implement the (static) method DialingCodes.GetCountryNameFromDictionary() that takes a dialing code and returns the corresponding country name. If the dialing code is not contained in the dictionary then an empty string is returned.

DialingCodes.GetCountryNameFromDictionary(
  DialingCodes.GetExistingDictionary(), 55);
// => "Brazil"

DialingCodes.GetCountryNameFromDictionary(
  DialingCodes.GetExistingDictionary(), 999);
// => string.Empty

6. Check that a country exists in the dictionary

Implement the (static) method DialingCodes.CheckCodeExists() to check whether a dialing code exists in the dictionary.

DialingCodes.CheckCodeExists(DialingCodes.GetExistingDictionary(), 55);
// => true

7. Update a country name

Implement the (static) method DialingCodes.UpdateDictionary() which takes a dialing code and replaces the corresponding country name in the dictionary with the country name passed as a parameter. If the dialing code does not exist in the dictionary then the dictionary remains unchanged.

DialingCodes.UpdateDictionary(
  DialingCodes.GetExistingDictionary(), 1, "Les États-Unis");
// => 1 => "Les États-Unis", 55 => "Brazil", 91 => "India"

DialingCodes.UpdateDictionary(
  DialingCodes.GetExistingDictionary(), 999, "Newlands");
// 1 => "United States of America", 55 => "Brazil", 91 => "India"

8. Remove a country from the dictionary

Implement the (static) method DialingCodes.RemoveCountryFromDictionary() that takes a dialing code and will remove the corresponding record, dialing code + country name, from the dictionary.

DialingCodes.RemoveCountryFromDictionary(
  DialingCodes.GetExistingDictionary(), 91);
// => 1 => "United States of America", 55 => "Brazil"

9. Find the country with the longest name

Implement the (static) method DialingCodes.FindLongestCountryName() which will return the name of the country with the longest name stored in the dictionary.

DialingCodes.FindLongestCountryName(
  DialingCodes.GetExistingDictionary());
// => "United States of America"

Source

Created by

• @mikedamay

Contributed to by

• @ErikSchierboom
• @valentin-p
• @yzAlvin