Stack and Queue added to new folder Data Structures

Competitive Coding/Data Structures/Queue/queue.java

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+package Data_Structures;
+import java.util.*;
+class Queue
+{
+	private int q[], front, rear, size;
+
+
+	/***** Constructor to initialize queue *****/
+	queue(int n)
+	{ //Begin constructor
+		size = n;
+		front = -1;
+		rear = -1;
+		q = new int[size];
+
+		for(int i = 0; i<size; i++)
+			q[i] = 0;	
+	} //end constructor
+
+
+
+	/***** Fucntion to insert an item to queue *****/
+	private void insert(int item)
+	{ //Begin insert()
+		if(rear == (size-1)) //Checks if rear pointer has reached the last limit (Queue is completely full or not) 
+		{
+			System.out.println("Queue Overflow");
+		}
+
+		elseif(front == -1 && rear == -1) //Checks if queue is empty to insert the very first element
+		{
+			front = 0; rear = 0;				
+			q[rear] = item;
+		}
+
+		else
+		{
+			rear+=1;
+			q[rear] = item;
+		}
+
+	} //End insert()
+
+
+
+
+	/***** Fucntion to delete an item from queue *****/
+	private void delete()
+	{ //Begin delete()
+
+
+			if(front == -1 && rear == -1) //Checks if queue is empty
+			{
+				System.out.println("Queue Underflow");	
+			}
+
+
+
+
+			elseif(front == rear) //Checks if only one element is present
+			{
+				System.out.println("Deleted element:\t"+q[front]);
+				front = -1; rear = -1;				
+			}
+
+			else
+			{
+				System.out.println("Deleted element:\t"+q[front]);					
+				front += 1;
+			}			
+
+	} //End delete()
+
+
+
+	/***** Function to display the elements of the queue *****/
+	private void display()
+	{ //Begin display()
+		if(front == - 1 && rear == -1)
+		{
+			System.out.println("Queue is EMPTY");
+		}
+
+		else
+		{
+			System.out.print("Elements of the queue:\nfront ---> ");
+
+			for(int i = front; i <= rear; i++)
+				System.out.print(q[i]+"\t");
+
+			System.out.println("<--- rear");
+
+		}
+	} //End display()
+
+
+
+
+	public static void main(String args[])
+	{ //Begin main()
+
+		Scanner sc = new Scanner(System.in);
+		System.out.println("Enter the size of the queue");
+		int n = sc.nextInt();
+
+		queue q1 = new queue(n);
+
+		int choice;
+		do
+		{ //Begin do
+			System.out.println("\nEnter:\n1. Insert\n2. Delete\n3. Display");
+			choice = sc.nextInt();
+			switch(choice)
+			{ //Begin switch
+				case 1: System.out.println("\nEnter an element to insert");
+					int element = sc.nextInt();
+					q1.insert(element);
+					break;
+
+				case 2: q1.delete();
+					break;
+
+				case 3: q1.display();
+					break;
+
+				default: System.out.println("Wrong choice. Exitting.");
+					break;
+			} //End switch
+		} //End do
+		while(choice >= 1 && choice <= 3);
+	} //End main()
+} //End class

Competitive Coding/Data Structures/Stack/stack.java

@@ -0,0 +1,130 @@
+package Data_Structures
+import java.util.*;
+class stack
+{ //Begin class
+
+	int top = -1, size, s[];
+
+
+	/*****Constructor to initialise the stack *****/
+	stack(int n)
+	{ //Begin constructor
+		size = n;
+
+		s = new int[size];		
+		for(int i = 0; i < size; i++)
+		{ //Begin for
+			s[i] = 0;
+		} //End for			
+	} //End constructor
+
+
+
+	/***** Fucntion to insert/push item to stack *****/
+	private void push(int item)
+	{ //Begin push()
+
+		if(top == (size-1)) //Checks if stack is full
+		{ //Begin if
+			System.out.println("Stack overflow");
+		} //End if
+
+		else //Element is entered to the stack when there is place
+		{ //Begin else
+			top++;
+			s[top] = item;
+		} //End else
+
+	} //End push()
+
+
+
+	/***** Function to delete/pop an item (topmost element) from stack *****/
+	private void pop()
+	{ //Begin pop()
+
+		if(top == -1) //Checks if stack is empty
+		{ //Begin if
+			System.out.println("Stack underflow");
+		} //End if
+
+		else
+		{ //Begin else
+			System.out.println("Item deleted is:\t"+s[top]);
+			top--;
+		} //End else
+	} //End pop()
+
+
+	/***** Function to peep (show the topmost element in stack) *****/
+	private void peep()
+	{ //Begin peep()
+		if(top == -1)
+			System.out.println("No element to peep");
+
+		else
+			System.out.println("Peep: top ---> "+s[top]);
+	} //End peep()
+
+
+
+	/***** Function to display the elements of stack *****/
+	private void display()
+	{ //Begin display()
+
+		if(top == -1)
+		{ //Begin if
+			System.out.println("No elements in stack");
+		} //End if
+
+		else
+		{ //Begin else
+
+			System.out.print("Elements of the stack: top---> ");
+			for(int i=top; i>=0; i--)
+			{
+				System.out.print(s[i]+"\t");
+			}
+			System.out.println();
+		} //End else
+	} //End display()
+
+
+	/***** main fucntion *****/
+	public static void main(String args[])
+	{ //Begin main()
+
+		Scanner sc = new Scanner(System.in);
+		System.out.println("Enter the size of the stack");
+		int n = sc.nextInt();
+
+		stack st = new stack(n);
+
+		int choice;
+		do
+		{ //Begin do
+			System.out.println("\nEnter:\n1. Push\n2. Pop\n3. Peep\n4. Display");
+			choice = sc.nextInt();
+			switch(choice)
+			{ //Begin switch
+				case 1: System.out.println("\nEnter an element to push");
+					int element = sc.nextInt();
+					st.push(element);
+					break;
+
+				case 2: st.pop();
+					break;
+
+				case 3: st.peep();
+					break;
+
+				case 4: st.display();
+					break;
+
+				default: System.out.println("Wrong choice. Exitting!");
+					break;
+			} //End switch
+		} //End do
+		while(choice >= 1 && choice <= 4);
+	} //End main()
+} //End class