Generating all possible subsequences

Here given code implementation process.

// C program 
// Generating all possible subsequences
#include <stdio.h>
#include <stdlib.h>

struct MyStack
{
	int element;
	struct MyStack *next;
};

//Add a new element into stack
void push(struct MyStack **top, int data)
{
	//Make a new node
	struct MyStack *new_node = (struct MyStack *) malloc(sizeof(struct MyStack));
	if (new_node != NULL)
	{
		//Set node values
		new_node->element = data;
		new_node->next = *top;*top = new_node;
	}
	else
	{
		printf("Memory Overflow\n");
	}
}
// Remove stack element
void pop(struct MyStack **top)
{
	if ( *top != NULL)
	{
		struct MyStack *temp = *top;*top = temp->next;
		free(temp);
		temp = NULL;
	}
}
// Display given array elements
void display(int collection[], int size)
{
	printf("\n Given collection \n ");
	for (int i = 0; i < size; ++i)
	{
		printf(" %d ", collection[i]);
	}
}
//Display subsequences 
void print_element(struct MyStack *top)
{
	struct MyStack *temp = top;
	printf(" [");
	//Display stack elements
	while (temp != NULL)
	{
		printf(" %d ", temp->element);
		//visit to next node
		temp = temp->next;
	}
	printf("]\n");
}
//Recursive finding all elements of subsequences
void all_subsequences(int collection[], struct MyStack **top, int location)
{
	if (location == -1)
	{
		//Print the sub-sequences, with empty sequences
		print_element( *top);
	}
	else
	{
		all_subsequences(collection, top, location - 1);
		// Add a element into stack  
		push(top, collection[location]);
		all_subsequences(collection, top, location - 1);
		// Remove a stack element
		pop(top);
	}
}
// Handles the request to print subsequence element
void subsequences(int collection[], int size)
{
	if (size <= 0)
	{
		return;
	}
	// Display given collection elements
	display(collection, size);
	//Create a stack variable
	struct MyStack *top = NULL;
	printf("\n All subsequences \n");
	all_subsequences(collection, &top, size - 1);
}
int main()
{
	int arr[] = {
		1 , 2 , 3 , 4
	};
	//Get the size
	int size = sizeof(arr) / sizeof(arr[0]);
	subsequences(arr, size);
	return 0;
}

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
/* 
  Java program 
  Print all subsequences of given size
*/
//Stack Node
class Node
{
	public int data;
	public Node next;
	public Node(int data)
	{
		this.data = data;
		this.next = null;
	}
}
//Define custom stack and its operation
class MyStack
{
	public Node top;
	public MyStack()
	{
		this.top = null;
	}
	//Add a new element in stack
	public void push(int data)
	{
		//Make a new stack node
		Node new_node = new Node(data);
		if (new_node != null)
		{
			new_node.next = this.top;
			this.top = new_node;
		}
		else
		{
			System.out.print("Memory overflow\n");
		}
	}
	//remove a top element in stack
	public void pop()
	{
		if (this.top != null)
		{
			this.top = this.top.next;
		}
	}
	//check that whether stack is empty or not
	public boolean is_empty()
	{
		if (this.top != null)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	public int peek()
	{
		if (this.top != null)
		{
			return this.top.data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence
{
	public MyStack stack;
	public Subsequence()
	{
		stack = new MyStack();
	}
	// Display given array elements
	public void display(int[] collection, int size)
	{
		System.out.print("\n Given collection \n ");
		for (int i = 0; i < size; ++i)
		{
			System.out.print(" " + collection[i] + " ");
		}
	}
	//Display subsequences 
	public void print_element()
	{
		Node temp = this.stack.top;
		System.out.print(" [");
		//Display stack elements
		while (temp != null)
		{
			System.out.print(" " + temp.data + " ");
			//visit to next node
			temp = temp.next;
		}
		System.out.print("]\n");
	}
	//Recursive finding all elements of subsequences
	public void all_subsequences(int[] collection, int location)
	{
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			print_element();
		}
		else
		{
			all_subsequences(collection, location - 1);
			// Add a element into stack  
			this.stack.push(collection[location]);
			all_subsequences(collection, location - 1);
			// Remove a stack element
			this.stack.pop();
		}
	}
	// Handles the request to print subsequence element
	public void subsequences(int[] collection, int size)
	{
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		display(collection, size);
		System.out.print("\n All subsequences \n");
		all_subsequences(collection, size - 1);
	}
	public static void main(String[] args)
	{
		Subsequence obj = new Subsequence();
		int[] arr = {
			1 , 2 , 3 , 4
		};
		//Get the size
		int size = arr.length;
		obj.subsequences(arr, size);
	}
}

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
//Include header file
#include <iostream>
using namespace std;

/*
  C++ program 
  Print all subsequences of given size
*/

//Stack Node
class Node
{
	public: 
    int data;
	Node *next;
	Node(int data)
	{
		this->data = data;
		this->next = NULL;
	}
};
//Define custom stack and its operation
class MyStack
{
	public: 
    Node *top;
	MyStack()
	{
		this->top = NULL;
	}
	//Add a new element in stack
	void push(int data)
	{
		//Make a new stack node
		Node *new_node = new Node(data);
		if (new_node != NULL)
		{
			new_node->next = this->top;
			this->top = new_node;
		}
		else
		{
			cout << "Memory overflow\n";
		}
	}
	//remove a top element in stack
	void pop()
	{
		if (this->top != NULL)
		{
			this->top = this->top->next;
		}
	}
	//check that whether stack is empty or not
	bool is_empty()
	{
		if (this->top != NULL)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	int peek()
	{
		if (this->top != NULL)
		{
			return this->top->data;
		}
		else
		{
			return 0;
		}
	}
};
class Subsequence
{
	public: MyStack *stack;
	Subsequence()
	{
		this->stack = new MyStack();
	}
	// Display given array elements
	void display(int collection[], int size)
	{
		cout << "\n Given collection \n ";
		for (int i = 0; i < size; ++i)
		{
			cout << " " << collection[i] << " ";
		}
	}
	//Display subsequences 
	void print_element()
	{
		Node *temp = this->stack->top;
		cout << " [";
		//Display stack elements
		while (temp != NULL)
		{
			cout << " " << temp->data << " ";
			//visit to next node
			temp = temp->next;
		}
		cout << "]\n";
	}
	//Recursive finding all elements of subsequences
	void all_subsequences(int collection[], int location)
	{
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			this->print_element();
		}
		else
		{
			this->all_subsequences(collection, location - 1);
			// Add a element into stack  
			this->stack->push(collection[location]);
			this->all_subsequences(collection, location - 1);
			// Remove a stack element
			this->stack->pop();
		}
	}
	// Handles the request to print subsequence element
	void subsequences(int collection[], int size)
	{
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		this->display(collection, size);
		cout << "\n All subsequences \n";
		this->all_subsequences(collection, size - 1);
	}
};
int main()
{
	Subsequence obj = Subsequence();
	int arr[] = {
		1 , 2 , 3 , 4
	};
	//Get the size
	int size = sizeof(arr) / sizeof(arr[0]);
	obj.subsequences(arr, size);
	return 0;
}

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
//Include namespace system
using System;

/* 
  C# program 
  Print all subsequences of given size
*/

//Stack Node
class Node
{
	public int data;
	public Node next;
	public Node(int data)
	{
		this.data = data;
		this.next = null;
	}
}
//Define custom stack and its operation
class MyStack
{
	public Node top;
	public MyStack()
	{
		this.top = null;
	}
	//Add a new element in stack
	public void push(int data)
	{
		//Make a new stack node
		Node new_node = new Node(data);
		if (new_node != null)
		{
			new_node.next = this.top;
			this.top = new_node;
		}
		else
		{
			Console.Write("Memory overflow\n");
		}
	}
	//remove a top element in stack
	public void pop()
	{
		if (this.top != null)
		{
			this.top = this.top.next;
		}
	}
	//check that whether stack is empty or not
	public Boolean is_empty()
	{
		if (this.top != null)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	public int peek()
	{
		if (this.top != null)
		{
			return this.top.data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence
{
	public MyStack stack;
	public Subsequence()
	{
		stack = new MyStack();
	}
	// Display given array elements
	public void display(int[] collection, int size)
	{
		Console.Write("\n Given collection \n ");
		for (int i = 0; i < size; ++i)
		{
			Console.Write(" " + collection[i] + " ");
		}
	}
	//Display subsequences 
	public void print_element()
	{
		Node temp = this.stack.top;
		Console.Write(" [");
		//Display stack elements
		while (temp != null)
		{
			Console.Write(" " + temp.data + " ");
			//visit to next node
			temp = temp.next;
		}
		Console.Write("]\n");
	}
	//Recursive finding all elements of subsequences
	public void all_subsequences(int[] collection, int location)
	{
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			print_element();
		}
		else
		{
			all_subsequences(collection, location - 1);
			// Add a element into stack  
			this.stack.push(collection[location]);
			all_subsequences(collection, location - 1);
			// Remove a stack element
			this.stack.pop();
		}
	}
	// Handles the request to print subsequence element
	public void subsequences(int[] collection, int size)
	{
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		display(collection, size);
		Console.Write("\n All subsequences \n");
		all_subsequences(collection, size - 1);
	}
	public static void Main(String[] args)
	{
		Subsequence obj = new Subsequence();
		int[] arr = {
			1 , 2 , 3 , 4
		};
		//Get the size
		int size = arr.Length;
		obj.subsequences(arr, size);
	}
}

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
<?php
/* 
  Php program 
  Print all subsequences of given size
*/
//Stack Node
class Node
{
	public $data;
	public $next;

	function __construct($data)
	{
		$this->data = $data;
		$this->next = null;
	}
}
//Define custom stack and its operation
class MyStack
{
	public $top;

	function __construct()
	{
		$this->top = null;
	}
	//Add a new element in stack
	public	function push($data)
	{
		//Make a new stack node
		$new_node = new Node($data);
		if ($new_node != null)
		{
			$new_node->next = $this->top;
			$this->top = $new_node;
		}
		else
		{
			echo "Memory overflow\n";
		}
	}
	//remove a top element in stack
	public	function pop()
	{
		if ($this->top != null)
		{
			$this->top = $this->top->next;
		}
	}
	//check that whether stack is empty or not
	public	function is_empty()
	{
		if ($this->top != null)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	public	function peek()
	{
		if ($this->top != null)
		{
			return $this->top->data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence
{
	public $stack;

	function __construct()
	{
		$this->stack = new MyStack();
	}
	// Display given array elements
	public	function display( & $collection, $size)
	{
		echo "\n Given collection \n ";
		for ($i = 0; $i < $size; ++$i)
		{
			echo " ". $collection[$i] ." ";
		}
	}
	//Display subsequences 
	public	function print_element()
	{
		$temp = $this->stack->top;
		echo " [";
		//Display stack elements
		while ($temp != null)
		{
			echo " ". $temp->data ." ";
			//visit to next node
			$temp = $temp->next;
		}
		echo "]\n";
	}
	//Recursive finding all elements of subsequences
	public	function all_subsequences( & $collection, $location)
	{
		if ($location == -1)
		{
			//Print the sub-sequences, with empty sequences
			$this->print_element();
		}
		else
		{
			$this->all_subsequences($collection, $location - 1);
			// Add a element into stack  
			$this->stack->push($collection[$location]);
			$this->all_subsequences($collection, $location - 1);
			// Remove a stack element
			$this->stack->pop();
		}
	}
	// Handles the request to print subsequence element
	public	function subsequences( & $collection, $size)
	{
		if ($size <= 0)
		{
			return;
		}
		// Display given collection elements
		$this->display($collection, $size);
		echo "\n All subsequences \n";
		$this->all_subsequences($collection, $size - 1);
	}
}

function main()
{
	$obj = new Subsequence();
	$arr = array(1, 2, 3, 4);
	//Get the size
	$size = count($arr);
	$obj->subsequences($arr, $size);
}
main();

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
/* 
  Node Js program 
  Print all subsequences of given size
*/
//Stack Node
class Node
{
	constructor(data)
	{
		this.data = data;
		this.next = null;
	}
}
//Define custom stack and its operation
class MyStack
{
	constructor()
	{
		this.top = null;
	}
	//Add a new element in stack
	push(data)
	{
		//Make a new stack node
		var new_node = new Node(data);
		if (new_node != null)
		{
			new_node.next = this.top;
			this.top = new_node;
		}
		else
		{
			process.stdout.write("Memory overflow\n");
		}
	}
	//remove a top element in stack
	pop()
	{
		if (this.top != null)
		{
			this.top = this.top.next;
		}
	}
	//check that whether stack is empty or not
	is_empty()
	{
		if (this.top != null)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	peek()
	{
		if (this.top != null)
		{
			return this.top.data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence
{
	constructor()
	{
		this.stack = new MyStack();
	}
	// Display given array elements
	display(collection, size)
	{
		process.stdout.write("\n Given collection \n ");
		for (var i = 0; i < size; ++i)
		{
			process.stdout.write(" " + collection[i] + " ");
		}
	}
	//Display subsequences 
	print_element()
	{
		var temp = this.stack.top;
		process.stdout.write(" [");
		//Display stack elements
		while (temp != null)
		{
			process.stdout.write(" " + temp.data + " ");
			//visit to next node
			temp = temp.next;
		}
		process.stdout.write("]\n");
	}
	//Recursive finding all elements of subsequences
	all_subsequences(collection, location)
	{
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			this.print_element();
		}
		else
		{
			this.all_subsequences(collection, location - 1);
			// Add a element into stack  
			this.stack.push(collection[location]);
			this.all_subsequences(collection, location - 1);
			// Remove a stack element
			this.stack.pop();
		}
	}
	// Handles the request to print subsequence element
	subsequences(collection, size)
	{
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		this.display(collection, size);
		process.stdout.write("\n All subsequences \n");
		this.all_subsequences(collection, size - 1);
	}
}

function main()
{
	var obj = new Subsequence();
	var arr = [1, 2, 3, 4];
	//Get the size
	var size = arr.length;
	obj.subsequences(arr, size);
}
main();

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
#   Python 3 program 
#   Print all subsequences of given size

# Stack Node
class Node :
	
	def __init__(self, data) :
		self.data = data
		self.next = None
	

# Define custom stack and its operation
class MyStack :
	
	def __init__(self) :
		self.top = None
	
	# Add a new element in stack
	def push(self, data) :
		# Make a new stack node
		new_node = Node(data)
		if (new_node != None) :
			new_node.next = self.top
			self.top = new_node
		else :
			print("Memory overflow\n", end = "")
		
	
	# remove a top element in stack
	def pop(self) :
		if (self.top != None) :
			self.top = self.top.next
		
	
	# check that whether stack is empty or not
	def is_empty(self) :
		if (self.top != None) :
			return False
		else :
			return True
		
	
	# Used to get top element of stack
	def peek(self) :
		if (self.top != None) :
			return self.top.data
		else :
			return 0
		
	

class Subsequence :
	
	def __init__(self) :
		self.stack = MyStack()
	
	#  Display given array elements
	def display(self, collection, size) :
		print("\n Given collection \n ", end = "")
		i = 0
		while (i < size) :
			print(" ", collection[i] ," ", end = "")
			i += 1
		
	
	# Display subsequences 
	def print_element(self) :
		temp = self.stack.top
		print(" [", end = "")
		# Display stack elements
		while (temp != None) :
			print(" ", temp.data ," ", end = "")
			# visit to next node
			temp = temp.next
		
		print("]\n", end = "")
	
	# Recursive finding all elements of subsequences
	def all_subsequences(self, collection, location) :
		if (location == -1) :
			# Print the sub-sequences, with empty sequences
			self.print_element()
		else :
			self.all_subsequences(collection, location - 1)
			#  Add a element into stack  
			self.stack.push(collection[location])
			self.all_subsequences(collection, location - 1)
			#  Remove a stack element
			self.stack.pop()
		
	
	#  Handles the request to print subsequence element
	def subsequences(self, collection, size) :
		if (size <= 0) :
			return
		
		#  Display given collection elements
		self.display(collection, size)
		print("\n All subsequences \n", end = "")
		self.all_subsequences(collection, size - 1)
	

def main() :
	obj = Subsequence()
	arr = [1, 2, 3, 4]
	# Get the size
	size = len(arr)
	obj.subsequences(arr, size)

if __name__ == "__main__": main()

Output

 Given collection
   1    2    3    4
 All subsequences
 []
 [  1  ]
 [  2  ]
 [  1    2  ]
 [  3  ]
 [  1    3  ]
 [  2    3  ]
 [  1    2    3  ]
 [  4  ]
 [  1    4  ]
 [  2    4  ]
 [  1    2    4  ]
 [  3    4  ]
 [  1    3    4  ]
 [  2    3    4  ]
 [  1    2    3    4  ]
#   Ruby program 
#   Print all subsequences of given size

# Stack Node
class Node  
    # Define the accessor and reader of class Node  
    attr_reader :data, :next
    attr_accessor :data, :next
 
    
    def initialize(data) 
        self.data = data
        self.next = nil
    end

end

# Define custom stack and its operation
class MyStack  
    # Define the accessor and reader of class MyStack  
    attr_reader :top
    attr_accessor :top
 
    
    def initialize() 
        self.top = nil
    end

    # Add a new element in stack
    def push(data) 
        # Make a new stack node
        new_node = Node.new(data)
        if (new_node != nil) 
            new_node.next = self.top
            self.top = new_node
        else 
            print("Memory overflow\n")
        end

    end

    # remove a top element in stack
    def pop() 
        if (self.top != nil) 
            self.top = self.top.next
        end

    end

    # check that whether stack is empty or not
    def is_empty() 
        if (self.top != nil) 
            return false
        else 
            return true
        end

    end

    # Used to get top element of stack
    def peek() 
        if (self.top != nil) 
            return self.top.data
        else 
            return 0
        end

    end

end

class Subsequence  
    # Define the accessor and reader of class Subsequence  
    attr_reader :stack
    attr_accessor :stack
 
    
    def initialize() 
        self.stack = MyStack.new()
    end

    #  Display given array elements
    def display(collection, size) 
        print("\n Given collection \n ")
        i = 0
        while (i < size) 
            print(" ", collection[i] ," ")
            i += 1
        end

    end

    # Display subsequences 
    def print_element() 
        temp = self.stack.top
        print(" [")
        # Display stack elements
        while (temp != nil) 
            print(" ", temp.data ," ")
            # visit to next node
            temp = temp.next
        end

        print("]\n")
    end

    # Recursive finding all elements of subsequences
    def all_subsequences(collection, location) 
        if (location == -1) 
            # Print the sub-sequences, with empty sequences
            self.print_element()
        else 
            self.all_subsequences(collection, location - 1)
            #  Add a element into stack  
            self.stack.push(collection[location])
            self.all_subsequences(collection, location - 1)
            #  Remove a stack element
            self.stack.pop()
        end

    end

    #  Handles the request to print subsequence element
    def subsequences(collection, size) 
        if (size <= 0) 
            return
        end

        #  Display given collection elements
        self.display(collection, size)
        print("\n All subsequences \n")
        self.all_subsequences(collection, size - 1)
    end

end

def main() 
    obj = Subsequence.new()
    arr = [1, 2, 3, 4]
    # Get the size
    size = arr.length
    obj.subsequences(arr, size)
end

main()

Output

 Given collection 
  1  2  3  4 
 All subsequences 
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
/* 
  Scala program 
  Print all subsequences of given size
*/

//Stack Node
class Node(var data: Int,
	var next: Node)
{
	def this(data: Int)
	{
		this(data, null);
	}
}
//Define custom stack and its operation
class MyStack(var top: Node)
{
	def this()
	{
		this(null);
	}
	//Add a new element in stack
	def push(data: Int): Unit = {
		//Make a new stack node
		var new_node: Node = new Node(data);
		if (new_node != null)
		{
			new_node.next = this.top;
			this.top = new_node;
		}
		else
		{
			print("Memory overflow\n");
		}
	}
	//remove a top element in stack
	def pop(): Unit = {
		if (this.top != null)
		{
			this.top = this.top.next;
		}
	}
	//check that whether stack is empty or not
	def is_empty(): Boolean = {
		if (this.top != null)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	def peek(): Int = {
		if (this.top != null)
		{
			return this.top.data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence(var stack: MyStack)
{
	def this()
	{
		this(new MyStack());
	}
	// Display given array elements
	def display(collection: Array[Int], size: Int): Unit = {
		print("\n Given collection \n ");
		var i: Int = 0;
		while (i < size)
		{
			print(" " + collection(i) + " ");
			i += 1;
		}
	}
	//Display subsequences 
	def print_element(): Unit = {
		var temp: Node = this.stack.top;
		print(" [");
		//Display stack elements
		while (temp != null)
		{
			print(" " + temp.data + " ");
			//visit to next node
			temp = temp.next;
		}
		print("]\n");
	}
	//Recursive finding all elements of subsequences
	def all_subsequences(collection: Array[Int], location: Int): Unit = {
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			print_element();
		}
		else
		{
			all_subsequences(collection, location - 1);
			// Add a element into stack  
			this.stack.push(collection(location));
			all_subsequences(collection, location - 1);
			// Remove a stack element
			this.stack.pop();
		}
	}
	// Handles the request to print subsequence element
	def subsequences(collection: Array[Int], size: Int): Unit = {
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		display(collection, size);
		print("\n All subsequences \n");
		all_subsequences(collection, size - 1);
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var obj: Subsequence = new Subsequence();
		var arr: Array[Int] = Array(1, 2, 3, 4);
		//Get the size
		var size: Int = arr.length;
		obj.subsequences(arr, size);
	}
}

Output

 Given collection
  1  2  3  4
 All subsequences
 []
 [ 1 ]
 [ 2 ]
 [ 1  2 ]
 [ 3 ]
 [ 1  3 ]
 [ 2  3 ]
 [ 1  2  3 ]
 [ 4 ]
 [ 1  4 ]
 [ 2  4 ]
 [ 1  2  4 ]
 [ 3  4 ]
 [ 1  3  4 ]
 [ 2  3  4 ]
 [ 1  2  3  4 ]
/* 
  Swift 4 program 
  Print all subsequences of given size
*/

//Stack Node
class Node
{
	var data: Int;
	var next: Node? ;
	init(_ data: Int)
	{
		self.data = data;
		self.next = nil;
	}
}
//Define custom stack and its operation
class MyStack
{
	var top: Node? ;
	init()
	{
		self.top = nil;
	}
	//Add a new element in stack
	func push(_ data: Int)
	{
		//Make a new stack node
		let new_node: Node? = Node(data);
		if (new_node != nil)
		{
			new_node!.next = self.top;
			self.top = new_node;
		}
		else
		{
			print("Memory overflow\n", terminator: "");
		}
	}
	//remove a top element in stack
	func pop()
	{
		if (self.top != nil)
		{
			self.top = self.top!.next;
		}
	}
	//check that whether stack is empty or not
	func is_empty() -> Bool
	{
		if (self.top != nil)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	//Used to get top element of stack
	func peek() -> Int
	{
		if (self.top != nil)
		{
			return self.top!.data;
		}
		else
		{
			return 0;
		}
	}
}
class Subsequence
{
	var stack: MyStack ;
	init()
	{
		self.stack = MyStack();
	}
	// Display given array elements
	func display(_ collection: [Int], _ size: Int)
	{
		print("\n Given collection \n ", terminator: "");
		var i: Int = 0;
		while (i < size)
		{
			print(" ", collection[i]," ", terminator: "");
			i += 1;
		}
	}
	//Display subsequences 
	func print_element()
	{
		var temp: Node? = self.stack.top;
		print(" [", terminator: "");
		//Display stack elements
		while (temp != nil)
		{
			print(" ", temp!.data ," ", terminator: "");
			//visit to next node
			temp = temp!.next;
		}
		print("]\n", terminator: "");
	}
	//Recursive finding all elements of subsequences
	func all_subsequences(_ collection: [Int], _ location: Int)
	{
		if (location == -1)
		{
			//Print the sub-sequences, with empty sequences
			self.print_element();
		}
		else
		{
			self.all_subsequences(collection, location - 1);
			// Add a element into stack  
			self.stack.push(collection[location]);
			self.all_subsequences(collection, location - 1);
			// Remove a stack element
			self.stack.pop();
		}
	}
	// Handles the request to print subsequence element
	func subsequences(_ collection: [Int], _ size: Int)
	{
		if (size <= 0)
		{
			return;
		}
		// Display given collection elements
		self.display(collection, size);
		print("\n All subsequences \n", terminator: "");
		self.all_subsequences(collection, size - 1);
	}
}
func main()
{
	let obj: Subsequence = Subsequence();
	let arr: [Int] = [1, 2, 3, 4];
	//Get the size
	let size: Int = arr.count;
	obj.subsequences(arr, size);
}
main();

Output

 Given collection
   1    2    3    4
 All subsequences
 []
 [  1  ]
 [  2  ]
 [  1    2  ]
 [  3  ]
 [  1    3  ]
 [  2    3  ]
 [  1    2    3  ]
 [  4  ]
 [  1    4  ]
 [  2    4  ]
 [  1    2    4  ]
 [  3    4  ]
 [  1    3    4  ]
 [  2    3    4  ]
 [  1    2    3    4  ]


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