HashSet<T>.Contains(T) Method

Definition

Namespace:

System.Collections.Generic

Assemblies:

netstandard.dll, System.Collections.dll

Source:

HashSet.cs

Determines whether a HashSet<T> object contains the specified element.

C#

public bool Contains(T item);

Parameters

item

T

The element to locate in the HashSet<T> object.

Returns

Boolean

true if the HashSet<T> object contains the specified element; otherwise, false.

Implements

Contains(T) Contains(T)

Examples

The following example demonstrates how to remove values from a HashSet<T> collection using the Remove method. In this example, the Contains method verifies that the set contains a value before removing it.

C#

HashSet<int> numbers = new HashSet<int>();

for (int i = 0; i < 20; i++) {
    numbers.Add(i);
}

// Display all the numbers in the hash table.
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Remove all odd numbers.
numbers.RemoveWhere(IsOdd);
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Check if the hash table contains 0 and, if so, remove it.
if (numbers.Contains(0)) {
    numbers.Remove(0);
}
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

bool IsOdd(int i)
{
    return ((i % 2) == 1);
}

void DisplaySet(HashSet<int> set)
{
    Console.Write("{");
    foreach (int i in set)
        Console.Write(" {0}", i);

    Console.WriteLine(" }");
}

// This example displays the following output:
//    numbers contains 20 elements: { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 }
//    numbers contains 10 elements: { 0 2 4 6 8 10 12 14 16 18 }
//    numbers contains 9 elements: { 2 4 6 8 10 12 14 16 18 }

Remarks

This method is an O(1) operation.

Applies to