JAVA

Hashset

//HashMap/HashSet in c Sharp
HashSet<int> numbers = new HashSet<int>();
// below are the methods
numbers.Add(2);
numbers.Remove(2);
//Removes all elements that match the conditions 
//defined by the specified predicate from a HashSet<T> collection.
numbers.RemoveWhere(Predicate<T>);
//Removes all elements from a HashSet<T> object.
numbers.Clear();
// Determines whether a HashSet<T> object contains the specified element
numbers.Contains(0);
// The collection of items to remove from the HashSet<T> object.
numbers.ExceptWith(anotherHashset);
// Modifies the current HashSet<T> object to contain only 
// elements that are present in that object and in the specified collection.
numbers.IntersectWith(IEnumerable<T>);
// Searches the set for a given value and 
//returns the equal value it finds, if any.
numbers.TryGetValue(T, T) 
numbers.UnionWith(IEnumerable<T>)  // 

hashset java

// Java program to demonstrate working of HashSet
import java.util.*;
  
class HashSetDemo {
  
    // Main Method
    public static void main(String[] args)
    {
        HashSet<String> h = new HashSet<String>();
  
        // Adding elements into HashSet usind add()
        h.add("India");
        h.add("Australia");
        h.add("South Africa");
        h.add("India"); // adding duplicate elements
  
        // Displaying the HashSet
        System.out.println(h);
        System.out.println("List contains India or not:"
                           + h.contains("India"));
  
        // Removing items from HashSet using remove()
        h.remove("Australia");
        System.out.println("List after removing Australia:"
                           + h);
  
        // Iterating over hash set items
        System.out.println("Iterating over list:");
        Iterator<String> i = h.iterator();
        while (i.hasNext())
            System.out.println(i.next());
    }
}

hashset java

HashSet<Integer> set = new HashSet<>();
set.add(1);
set.add(2);

if(set.contains(1)){
  print("hashset contains 1");
}
else{
   print("hashset doesn't contain 1");
}
//output
hashset contains 1

example of HashSet

Set<String> set = new HashSet<String>(list);

hashset usage

- HashSet can have null, order is not guaranteed
- HashSet is commonly used if you want to access elements randomly or store a list of items which cannot contain duplicate values

Java Creating a HashSet

// HashSet with 8 capacity and 0.75 load factor
HashSet<Integer> numbers = new HashSet<>(8, 0.75);

hashset

/*
 * Template for using hash set to find duplicates.
 */
boolean findDuplicates(List<Type> keys) {
    // Replace Type with actual type of your key
    Set<Type> hashset = new HashSet<>();
    for (Type key : keys) {
        if (hashset.contains(key)) {
            return true;
        }
        hashset.add(key);
    }
    return false;
}

hashset implementation

class MyHashSet {
private:
	vector<bool> table;
public:
	MyHashSet() : table(1e6 + 1, false) {}
	
	void add(int key) {
		table[key] = true;
	}
	
	void remove(int key) {
		table[key] = false;
	}
	
	bool contains(int key) {
		return table[key];
	}
};