C#
Summary - Generic collections
Combine List, Dictionary and Queue to write a task queue.
Summary - Generic collections
In this group you studied five generic collections in depth. List<T> is a dynamic array, Dictionary<K,V> a hash table, SortedDictionary<K,V> a sorted tree, Queue<T> a FIFO sequence, LinkedList<T> a doubly linked list.
Each collection serves a different strength: fast lookup, ordered iteration, end insertion, or memory efficiency. Now two small tasks let you combine them.
Exercise AddRange to a list, print Count
Use AddRange to add 4, 5, 6 to list below. Then print list.Count with Console.WriteLine.
Show example solution
Add three items with AddRange, then print Count.
Example solution:
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
var list = new List<int> { 1, 2, 3 };
list.AddRange(new[] { 4, 5, 6 });
Console.WriteLine(list.Count);
}
}
Exercise Check a key with ContainsKey
Use ContainsKey to check whether "apple" is in the prices dictionary below; print the result with Console.WriteLine.
Show example solution
ContainsKey returns a bool; print it with WriteLine.
Example solution:
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
var prices = new Dictionary<string, int>();
prices.Add("apple", 5);
prices.Add("pear", 3);
Console.WriteLine(prices.ContainsKey("apple"));
}
}
Choosing a collection
Choosing the right collection drives performance. For fast lookup pick Dictionary<K,V>, for ordered iteration SortedDictionary<K,V>, for a FIFO sequence Queue<T>, for fast end insertion LinkedList<T>.
The next group covers the iteration interfaces and the yield keyword, so you can write your own collection.
Test yourself
-
Unique and sorted keys?
- List<T>
- SortedDictionary<K,V>
- Queue<T>
- LinkedList<T>
Show answer
SortedDictionary<K,V> — Correct. SortedDictionary keeps unique keys in order.
-
Complete the sorted dictionary
var ordered = new Sorted____<string, int>();
Show answer
var ordered = new SortedDictionary<string, int>();
Next lesson: IEnumerable<T>
