Question

In an application write a method filterStack that takes a stack of integers as a parameter and filters its elements (in a new Stack) in a way that places the even elements at the bottom and the odd ones at the top. The original stack should remain unchanged. You should use a queue (only one queue) as a temporary storage. Use stack and queue operations only to solve this problem. No need to write the main method.
For example, if we apply the method filterStack to stack s1 below then the method returns the stack s2.

Answer 1

#include<string>
#include<stack>
#include<queue>
#include<iostream>
using namespace std;

void filterStack(stack <int> mainStack)
{
   queue<int> tempForOdd; //For storing odd elements of stack
   stack <int> newStack; // New stack in which bottom elements are of even numbers and top will be odd numbers

   while (mainStack.empty() != true)
   {
       int element = mainStack.top();
       mainStack.pop();

       if (element % 2 == 0) //If even we will push in new stack
       {
           newStack.push(element);

       }

       else
       {
           tempForOdd.push(element); // else if odd it will be pushed to queue which is temproray storage
       }
   }

   //As in queue we have odd elements and in newStack we have all even elements
   // Now we will push odd elements in newStack which will be on top of the even numbers

   while (tempForOdd.empty() != true)
   {
       int element = tempForOdd.front(); // It will tell the front element of queue
       tempForOdd.pop();                       // This will remove the front element from queue and front will point to the next element

       newStack.push(element);
   }

   //Printing newStack elements

   int i = 1;
   while (newStack.empty() != true)
   {
       cout << "element#" << i << "of filter Stack= " << newStack.top()<<endl;
       newStack.pop();
      
   }

  
}

//int main()
//{
//   stack<int> test;
//   int number;
//
//   for (int i = 0; i < 10; i++)
//   {
//       cout << "Enter element#" << i + 1<<" ";
//       cin >> number;
//       test.push(number);
//   }
//
//   filterStack(test);
//}

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