HashMap Methods

Part of the Logic & Flow section of Coddy's C# journey — lesson 52 of 66.

HashMap methods provide powerful ways to work with your dictionary data. Let's explore some common methods:

Check if a key exists in the dictionary:

Dictionary<string, int> inventory = new Dictionary<string, int>();
inventory.Add("apples", 25);

bool hasApples = inventory.ContainsKey("apples");
// hasApples will be true

Get all keys from the dictionary:

Dictionary<string, int> scores = new Dictionary<string, int>();
scores.Add("Alice", 95);
scores.Add("Bob", 87);

// Get all keys
Dictionary<string, int>.KeyCollection keys = scores.Keys;
foreach (string name in keys)
{
    Console.WriteLine(name);
}

Get all values from the dictionary:

// Get all values
Dictionary<string, int>.ValueCollection values = scores.Values;
foreach (int score in values)
{
    Console.WriteLine(score);
}

Remove an item from the dictionary:

scores.Remove("Bob");
// Dictionary now only contains Alice's score

Clear all items:

scores.Clear();
// Dictionary is now empty

Get the number of items in the dictionary using .Count:

Dictionary<string, int> scores = new Dictionary<string, int>();
scores.Add("Alice", 95);
scores.Add("Bob", 87);

int total = scores.Count;
Console.WriteLine(total);
// Output: 2

Challenge

Medium

Create a method named ProcessDictionary that takes a Dictionary<string, int> as an argument and performs the following operations:

Print Keys: followed by all keys (one per line)
Print Values: followed by all values (one per line)
Check if the dictionary contains the key "total" and print Contains 'total': True or Contains 'total': False
Remove the key "temp" if it exists
Print Count: followed by the count of items in the dictionary after these operations (use the .Count property of the dictionary)

Cheat sheet

Check if a key exists using ContainsKey():

bool hasKey = dictionary.ContainsKey("keyName");

Get all keys from a dictionary:

Dictionary<string, int>.KeyCollection keys = dictionary.Keys;
foreach (string key in keys)
{
    Console.WriteLine(key);
}

Get all values from a dictionary:

Dictionary<string, int>.ValueCollection values = dictionary.Values;
foreach (int value in values)
{
    Console.WriteLine(value);
}

Remove an item using Remove():

dictionary.Remove("keyName");

Clear all items using Clear():

dictionary.Clear();

Get the number of items using .Count:

int count = dictionary.Count;

Try it yourself

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

class Program
{
    static void ProcessDictionary(Dictionary<string, int> dict)
    {
        // Write your code here
    }
    // Ignore the main code, it converts string to a HashMap
    static void Main(string[] args)
    {
        Dictionary<string, int> inputDict = new Dictionary<string, int>();
        
        // Read first line to check if it's JSON format
        string firstLine = Console.ReadLine();
        
        // Check if input is in JSON format
        if (firstLine != null && firstLine.StartsWith("{") && firstLine.EndsWith("}"))
        {
            try
            {
                // Process JSON input
                string jsonContent = firstLine.Substring(1, firstLine.Length - 2);
                
                // Split by commas that are not inside quotes
                string pattern = @",(?=(?:[^""]*""[^""]*"")*[^""]*$)";
                string[] entries = Regex.Split(jsonContent, pattern);
                
                foreach (string entry in entries)
                {
                    // Extract key and value using regex
                    Match match = Regex.Match(entry, @"""([^""]+)""\s*:\s*(\d+)");
                    if (match.Success)
                    {
                        string keyMatch = match.Groups[1].Value;
                        int valueMatch = int.Parse(match.Groups[2].Value);
                        inputDict.Add(keyMatch, valueMatch);
                    }
                }
                
                ProcessDictionary(inputDict);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error parsing input: {ex.Message}");
            }
        }
        else
        {
            try
            {
                // Process traditional input format
                int n = int.Parse(firstLine);
                
                for (int i = 0; i < n; i++)
                {
                    string[] pair = Console.ReadLine().Split(':');
                    string key = pair[0];
                    int value = int.Parse(pair[1]);
                    inputDict.Add(key, value);
                }
                
                ProcessDictionary(inputDict);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error parsing input: {ex.Message}");
            }
        }
    }
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Logic & Flow

1Multi-dimensional Arrays

2D Arrays Basics Declaring and Initializing 2D Accessing 2D Array Elements Nested Loops with 2D Arrays Jagged Arrays Common Matrix Operations Recap - Multi-dimensional

4Flow Control Techniques

Early Returns Guard Clauses Jump Statements (goto)Break and Continue Flatten Nested Conditionals

7Logical Operators Advanced

Short-Circuit Evaluation Conditional Logical Operators Operator Precedence Recap - Advanced Operators

10HashMap Part 2

HashMap MethodsNested HashMap Recap - Manage Warehouse Recap - HashMap Operations