Java TreeSet Equivalent in C#
Last Updated :
20 Mar, 2025
In Java, TreeSet is one of the most important implementations of the SortedSet interface based on a Tree (red-black tree) as a data storage. The elements are sorted by a set using their natural order whether an explicit comparator is provided or not.
In C#, the SortedSet class is the closest equivalent to Java TreeSet. It is an ordered set of unique elements. SortedSet is a generic set with unique elements ordered by the natural ordering of the element or by an implemented comparer. Like TreeSet, it keeps the elements in sorted order using a self-balancing binary search tree (mostly like a red-black tree).
Java TreeSet vs C# SortedSet
| Features | Java TreeSet | C# SortedSet |
|---|
Data Structure | Red-Black Tree | Red-Black Tree |
|---|
Sorting | This is sorted by natural order or custom comparator. | This is sorted by natural order or custom comparer. |
|---|
Time Complexity | O(log n) | O(log n) |
|---|
Duplicates | It does not contain any duplicate element. | It also does not contain any duplicate elements. |
|---|
Thread Safety | Not thread-safe. | Not thread-safe. |
|---|
Note: C# does not have a built-in equivalent of Java’s TreeSet. The SortedSet class provides similar functionality, but Java's TreeSet has additional methods like headSet(), tailSet(), and subSet(), which are not directly available in C#.
Key Features of SortedSet:
- The elements are always sorted in ascending order by default, or according to a custom comparer.
- This ensures that all elements in the set are unique means there are no duplicates.
- It provides O(log n) time complexity for insertions and deletions.
- It supports standard set operations like union, intersection, and difference.
Usage of SortedSet in C#
Below is a simple example that demonstrates how to use SortedSet<T> in C#:
C#
// Demonstrating SortedSet in C#
using System;
using System.Collections.Generic;
class Geeks
{
static void Main()
{
// creating a SortedSet
// with integer elements
SortedSet<int> ss = new SortedSet<int>();
// Adding elements
ss.Add(6);
ss.Add(4);
ss.Add(2);
ss.Add(1);
// Iterating through the set
Console.WriteLine("SortedSet elements:");
foreach (int e in ss)
{
Console.WriteLine(e);
}
// Checking if an element exists
if (ss.Contains(2))
{
Console.WriteLine("Element 2 exists.");
}
// Removing an element
ss.Remove(6);
Console.WriteLine("After removing 6:");
foreach (int e in ss)
{
Console.WriteLine(e);
}
}
}
OutputSortedSet elements:
1
2
4
6
Element 2 exists.
After removing 6:
1
2
4
Custom Sorting with IComparer<T>
When we want to sort the elements in a custom order, we can use an IComparer<T> implementation at the time of creation of SortedSet.
Example:
C#
// Demonstrating Custom Sorting
using System;
using System.Collections.Generic;
class Geeks
{
static void Main()
{
// Custom comparer for descending order
SortedSet<int> ss = new SortedSet<int>(new DescendingComparer());
ss.Add(6);
ss.Add(4);
ss.Add(2);
ss.Add(1);
Console.WriteLine("SortedSet with custom comparer (descending order):");
foreach (int e in ss)
{
Console.WriteLine(e);
}
}
}
class DescendingComparer : IComparer<int>
{
public int Compare(int x, int y)
{
return y.CompareTo(x);
}
}
OutputSortedSet with custom comparer (descending order):
6
4
2
1
Set Operations
The SortedSet supports basic set operations such as union, intersection, and difference.
Example:
C#
// Basic Set operations
using System;
using System.Collections.Generic;
class Geeks
{
static void Main()
{
SortedSet<int> s1 = new SortedSet<int> { 1, 2, 3, 4 };
SortedSet<int> s2 = new SortedSet<int> { 2, 3, 7, 8 };
// Union
SortedSet<int> u = new SortedSet<int>(s1);
u.UnionWith(s2);
Console.WriteLine("Union:");
foreach (int e in u)
{
Console.WriteLine(e);
}
// Intersection
SortedSet<int> i = new SortedSet<int>(s1);
i.IntersectWith(s2);
Console.WriteLine("Intersection:");
foreach (int e in i)
{
Console.WriteLine(e);
}
// Difference
SortedSet<int> d = new SortedSet<int>(s1);
d.ExceptWith(s2);
Console.WriteLine("Difference:");
foreach (int e in d)
{
Console.WriteLine(e);
}
}
}
OutputUnion:
1
2
3
4
7
8
Intersection:
2
3
Difference:
1
4
Thread Safety
SortedSet in C# is not thread safe like Java TreeSet. But if we want thread-safe operations, we can use synchronization mechanisms like locks or we can use ConcurrentDictionary<TKet, TValue> with dummy values.
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