implemented stack using 2 queues

Author: anishsingh20

Data Structures/Stacks/StackUsing2Queues.cpp

@@ -0,0 +1,180 @@
+#include<iostream>
+#include<queue>
+
+
+using namespace std;
+
+
+//IMPLEMENTING STACK USING 2 QUEUES
+
+queue<int> q1;
+queue<int> q2;
+
+
+class Stack {
+	public:
+		void Push(int data); //Takes-O(1) time complexity
+		void Pop();//-Takes -O(n)- time complexity- as we transfer n items from Queue1 to Queue2
+		void Top();
+};
+
+
+
+void Stack::Push(int data) {
+	
+	if(q1.empty()) {
+		q2.push(data); //if queue 1 is empty, then enqueue data to queue 2
+	}
+	else { //otherwise enqueue data to queue1
+		q1.push(data); 
+	}
+	
+}
+
+
+void Stack::Pop() {
+	int i=0,size;
+	if(q1.empty() && q2.empty()) {
+		cout<<"The stack is empty"<<endl;
+		return;
+	}
+	
+	if(q2.empty()) { //case if queue1 is not empty
+		
+		size= q1.size();
+		while(i < q1.size()-1 )  //transfer n-1 items from queue1(storage Queue) to queue2(temporary queue)
+		{
+			q2.push(q1.front()); //enqueue n-1 items from Queue 1 to Queue2
+			q1.pop();
+			i++;
+		}
+		cout<<"Deleted "<<q1.front()<<" from top."<<endl; //queue1 now has only 1 item-which will be popped in LIFO fashion
+		 q1.pop();
+	}
+	
+	else {
+		size=q2.size();
+		
+		while(i < size-1) { //transfer n-1 items from Q2(storage queue) to Q1(temp queue) 
+			q1.push(q2.front()); //enqueue n-1 items from Queue2 to Queue1
+			q2.pop();
+			i++;
+		}
+		 cout<<"Deleted "<<q2.front()<<" from top."<<endl; // Queue2 now has only 1 item which is popped
+		 q2.pop();
+		
+	}
+	
+}
+
+
+void Stack::Top() {
+	int i=0,size,front;
+	if(q1.empty() && q2.empty()) {
+		cout<<"The stack is empty"<<endl;
+		return ;
+	}
+	
+	if(q2.empty()) { //case if queue1 is not empty
+		
+		size= q1.size();
+		while(i < q1.size()-1 )  //transfer n-1 items from queue1(storage Queue) to queue2(temporary queue)
+		{
+			q2.push(q1.front()); //enqueue n-1 items from Queue 1 to Queue2
+			q1.pop();
+			i++;
+		}
+		
+		front=q1.front(); //storing last element of storage queue Q1 in front
+		
+		cout<<"Top of stack is "<<front<<endl;
+	
+		//inserting last element of Q1 to Q2
+		q2.push(q1.front());
+		q1.pop();
+		
+		
+		//now again transfer all back to storage queue Q1(storage queue) and make Q2 empty
+		while(!q2.empty()) {
+			q1.push(q2.front()); //
+			q2.pop();
+			
+			
+		}
+			
+	}
+	
+	else {
+		size=q2.size();
+		
+		while(i < size-1) { //transfer n-1 items from Q2(storage queue) to Q1(temp queue) 
+			q1.push(q2.front()); //enqueue n-1 items from Queue2 to Queue1
+			q2.pop();
+			i++;
+		}
+		front = q2.front();
+		
+		cout<<"Top of stack is "<<front<<endl;
+		
+		 
+		//insert the last item in Q2(storage queue) to Q1(temp queue)
+		q1.push(q2.front());
+		q2.pop();
+		
+		
+		//now again transfer all items back to Q2(storage queue) and make Q1 empty
+		while(!q1.empty()) {
+			
+			q2.push(q1.front()); //
+			q1.pop();
+		
+			
+		}
+		 
+		 
+		
+	}
+	
+	
+}
+
+
+
+
+int main() 
+{
+	
+	Stack s;
+	int choice,data;
+	while(1)
+	{
+		
+		
+		cout<<"\n1)Insert\n2)Delete\n3)Top of stack\n4)Exit\n"<<endl;
+		cin>>choice;
+		
+		
+		switch(choice) {
+			
+			case 1: 
+				cout<<"Enter data :"<<endl;
+				cin>>data;
+				s.Push(data);
+				break;
+			case 2:
+				
+				s.Pop();
+				break;
+			case 3:
+				s.Top();
+				break;
+			
+			default:
+				exit(0);
+				break;
+				
+		}
+	}
+	
+	return 0;
+}