SortedMap Interface in C#

In C#, there is no direct equivalent to Java's SortedMap interface. However, C# provides the SortedList and SortedDictionary collections which offer similar functionality for maintaining key-value pairs in sorted order.

The SortedList collection in C# uses both a key and an index to access items. It combines the features of an array and a hash table, maintaining items in sorted order based on the key values. You can access items either by index (like an ArrayList) or by key (like a Hashtable).

Syntax

Following is the syntax for creating a SortedList −

SortedList sortedList = new SortedList();
SortedList<TKey, TValue> sortedList = new SortedList<TKey, TValue>();

Following is the syntax for adding and accessing elements −

sortedList.Add(key, value);
var value = sortedList[key];

Using SortedList with Keys

The following example demonstrates how to create a SortedList, add items, and display the keys −

using System;
using System.Collections;

class Program {
    static void Main(string[] args) {
        SortedList sl = new SortedList();
        sl.Add("ST2", "Three");
        sl.Add("ST0", "One");
        sl.Add("ST1", "Two");
        
        ICollection keys = sl.Keys;
        Console.WriteLine("Keys in sorted order:");
        foreach(string k in keys) {
            Console.WriteLine(k);
        }
    }
}

The output of the above code is −

Keys in sorted order:
ST0
ST1
ST2

Using Generic SortedList

The generic version provides type safety and better performance −

using System;
using System.Collections.Generic;

class Program {
    static void Main(string[] args) {
        SortedList<string, string> sl = new SortedList<string, string>();
        sl.Add("C", "Cat");
        sl.Add("A", "Apple");
        sl.Add("B", "Ball");
        
        Console.WriteLine("Key-Value pairs in sorted order:");
        foreach(KeyValuePair<string, string> pair in sl) {
            Console.WriteLine($"{pair.Key}: {pair.Value}");
        }
        
        Console.WriteLine($"\nAccessing by key 'B': {sl["B"]}");
        Console.WriteLine($"Accessing by index 1: {sl.Values[1]}");
    }
}

The output of the above code is −

Key-Value pairs in sorted order:
A: Apple
B: Ball
C: Cat

Accessing by key 'B': Ball
Accessing by index 1: Ball

SortedList vs SortedDictionary

Common Use Cases

SortedList is ideal when you need −

• Automatic sorting of key-value pairs

• Access by both key and index

• Memory-efficient storage

• Frequent lookups with occasional updates

Conclusion

While C# doesn't have Java's SortedMap interface, SortedList provides equivalent functionality for maintaining sorted key-value collections. It offers dual access methods and automatic sorting, making it suitable for scenarios requiring ordered data with efficient lookups.