WAP to Implement Stack using Queue Efficiently

It Can be Done using two Strategy by making push or pop oeration costly

Method A: By making Push Operation Costly
* push:
o if q1 is empty then simply add the item & return
else if q1 is not empty enqueue all items of queue1 in queue2, & then
enqueue given element in queue1
o Then enqueue all items from q2 to q1 again
this way names of queue1 and queue2
* pop:
o deqeue from queue1


Method B: By making Pop Operation Costly
* push:
o enqueue in queue1
* pop:
o while size of queue1 is bigger than 1, pipe dequeued items
from queue1 into queue2
o dequeue and return the last item of queue1, then switch the
names of queue1 and queue2



Obvious 2nd method is best because 1st moves all the element twice in in push operation

1st method implementation

import java.util.*;

class StackUsingQueues
{


Queue q1 = new LinkedList();
Queue q2 = new LinkedList();

public int pop()
{
if (q1.peek() == null) {
System.out.println("The stack is empty, nothing to return");
int i = 0;
return i;
} else {
int pop = q1.remove();
return pop;

}
}

public void push(int data) {

if (q1.peek() == null) {
q1.add(data);
} else {
for (int i = q1.size(); i > 0; i--) {
q2.add(q1.remove());
}
q1.add(data);
for (int j = q2.size(); j > 0; j--) {
q1.add(q2.remove());
}

}
}

public static void main(String[] args) {
StackUsingQueues s1 = new StackUsingQueues();
// Stack s1 = new Stack();
s1.push(1);
s1.push(2);
s1.push(3);
s1.push(4);
s1.push(5);
s1.push(6);
s1.push(7);

// s1.push(6);
System.out.println("1st = " + s1.pop());
System.out.println("2nd = " + s1.pop());
System.out.println("3rd = " + s1.pop());
System.out.println("4th = " + s1.pop());
System.out.println("5th = " + s1.pop());
System.out.println("6th = " + s1.pop());
System.out.println("7th = " + s1.pop());

}

}

2nd method--Need to Modify

import java.util.*;

class StackUsingQueues
{


Queue q1 = new LinkedList();
Queue q2 = new LinkedList();

public int pop()
{
if(q1.peek() == null)
{
System.out.println("The stack is empty, nothing to return");
int i = 0;
return i;
}
else
{
while(q1.size()>q2.size())
{
q2.add(q1.remove());
}
int size=1,pop=0;
while(size!=q1.size())
{
pop=q1.remove();
size++;
}

while(!q2.isEmpty())
{
q1.add(q2.remove());
}

return pop;

}
//return 0;
}

public void push(int data)
{
q1.add(data);
}

boolean emptys(Queue q)
{
return (q.size()==0);

}
public static void main(String[] args) {
StackUsingQueues s1 = new StackUsingQueues();

s1.push(1);
s1.push(2);
s1.push(3);
s1.push(4);
s1.push(5);
s1.push(6);
s1.push(7);

// s1.push(6);
System.out.println("1st = " + s1.pop());
System.out.println("2nd = " + s1.pop());
System.out.println("3rd = " + s1.pop());
System.out.println("4th = " + s1.pop());
System.out.println("5th = " + s1.pop());
System.out.println("6th = " + s1.pop());
System.out.println("7th = " + s1.pop());

}

}

Run here https://ideone.com/K1a3C