Merge pull request LetsGrowMoreCommunity#156 from suvrashaw/main

3. Implement Stack using Queue (QUEUE) LetsGrowMoreCommunity#51

Queue/Java/StackUsingQueue.java

@@ -0,0 +1,178 @@
+/**
+ Implement Stack using Queue.
+ ref. https://leetcode.com/problems/implement-stack-using-queues/
+ 
+ The java.util package's Queue interface is used to hold the components that will be processed in
+ FIFO (First In First Out) order. Each Stack operation makes use of functions from the interface's
+ LinkedList class.
+ 
+ Time Complexity of Push Operation: O(n) and Pop Operation: O(1)
+ Space Complexity: O(n)
+ Where n is the size of the Stack. Here, n = q.size();
+ */
+
+package suvrashaw;
+import java.util.*; //Importing the package
+public class StackUsingQueue{
+    Queue<Integer> q1 = new LinkedList<>(); //Uses the Queue Interface
+
+    void push(int val){ //Adding into the Stack.
+        q1.add(val); //Adding a new entry into the Stack.
+        for (int i = 0; i < q1.size(); i++) //Putting previous entries after the new one. (Enqueue)
+            q1.add(q1.remove()); //'front' elements added to the 'rear'. (Dequeue)
+    }
+
+    int pop(){ //Deleting from the Stack.
+	if (q1.isEmpty()){ //Checking if the Stack is empty.
+            System.out.println("Stack Underflow"); //Stack Empty Message.
+            return -1; //Terminating the method if the Stack is empty.
+	}
+	return q1.remove(); //Deleting an entry from the Stack.
+    }
+
+    int top(){ //Denotes the position of the top of the Stack.
+	if (q1.isEmpty()) //Checking if the Stack is empty.
+            return -1; //top = -1 when a stack is empty.
+        return q1.peek(); //If the Stack isn't empty,
+                          //returns the position of the top of the Stack.
+    }
+
+    boolean empty(){ //Method to check if the Stack is empty.
+        return q1.isEmpty(); //Returns true is the interface object is empty.
+    }
+
+    int getSize(){ //Method to check the Stack size.
+        return q1.size(); //Returns size of the interface object q1, our virtual stack.
+    }
+
+    public static void main(String[] args){  //Main Method
+        StackUsingQueue obj = new StackUsingQueue();
+        Scanner sc = new Scanner(System.in); 
+        while(true){ //Menu Driven
+            System.out.println("1. push");
+            System.out.println("2. pop");
+            System.out.println("3. check top");
+            System.out.println("4. if Empty");
+            System.out.println("5. size");
+            System.out.println("6. exit");
+            System.out.println("Give Choice"); //Menu
+            int choice = sc.nextInt(); //User Choice
+            switch (choice){
+                case 1 -> { //push function.
+                    System.out.println("Input Number: "); //User Input
+                    obj.push(sc.nextInt());
+                    }
+                case 2 -> System.out.println("Deleted Element: " + obj.pop()); //pop function.
+                case 3 -> System.out.println("top: " + obj.top()); //function to check top's position.  
+                case 4 -> System.out.println("Empty: " + obj.empty()); //function to check if the Stack is empty.
+                case 5 -> System.out.println("Size: " + obj.getSize()); //function to check Stack's size.
+                case 6 -> System.exit(0); //function to quit the program.
+                default -> System.out.println("Wrong Entry"); //Error Choice Check
+            }}}}
+
+/**
+Test Case
+
+compile-single:
+run-single:
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+1
+Input Number: 
+10
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+1
+Input Number: 
+20
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+3
+top: 10
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+2
+Deleted Element: 10
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+33
+Wrong Entry
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+3
+top: 20
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+5
+Size: 1
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+4
+Empty: false
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+2
+Deleted Element: 20
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+4
+Empty: true
+1. push
+2. pop
+3. check top
+4. if Empty
+5. size
+6. exit
+Give Choice
+6
+BUILD SUCCESSFUL (total time: 1 minute 19 seconds)*/