Stack & Queue interview Questions



1. Implement stack using Queue.
#include <iostream>
#include<queue>
using namespace std;
class MyStack
{
  queue<int>Q;
  public:
  void push(int value)
  {
    int size = Q.size();
    Q.push(value);
    for(int i =0;i<size;i++)
    {
        Q.push(Q.front());
        Q.pop();
    }
  }
  void pop()
  {
      if (!Q.empty())
      {
          Q.pop();
      }
  }
  bool empty()
  {
      return (Q.empty());
  }
  int top()
  {
      return (Q.front());
  }
  void printElement()
  {
      cout<<"Printing Queue Elements"<<endl;
      queue<int>temp = Q;
      while(!temp.empty())
      {
          cout<<temp.front()<<endl;
          temp.pop();
      }
  }
};
int main() {
    MyStack st;
    st.push(1);
    st.push(2);
    st.push(3);
    st.push(4);
    st.printElement();
    st.pop();
    st.printElement();
    return 0;
}
2. Implement two stack in an array

Please fix the issue with the below program, it is not giving the expected output.
// Online C++ compiler to run C++ program online
#include <iostream>
#include<queue>
using namespace std;
class MyStack
{
private:
  int *array;
  int ArraySize;
  int size1;
  int size2;
   int index1;
   int index2;
 public:
  MyStack(int size)
  {
      int *array = new int[size];
      this->ArraySize = size;
      size1 = 0;
      size2 = ArraySize - 1;
      cout<<"Size1 = "<<size1<<endl;
      cout<<"Size2 = "<<size2<<endl;
      index1 = 0;
      index2 = size - 1;
      for(int i =0;i<ArraySize;i++)
      {
          cout<<array[i]<<endl;
      }
      cout<<"constructor is called"<<endl;
  }
  void push1(int value)
  {
     if ((index1<ArraySize))
     {
         array[index1] = value;
         index1++;
     }
     else
     {
         cout<<"This stack is already full"<<endl;
     }
  }
  void pop1()
  {
      if (index1 == 0)
      {
          cout<<"Stack is empty"<<endl;
      }
      else
      {
          index1--;
      }
  }
  void push2(int value)
  {
    if ((index2)<ArraySize)
     {
         array[index2] = value;
         index2--;
     }
     else
     {
         cout<<"This stack is already full"<<endl;
     }
  }
  void pop2()
  {
     if (index2 == ArraySize - 1)
      {
          cout<<"Stack is empty"<<endl;
      }
      else
      {
          index2++;
      }
  }
  void SizeOfStack1()
  {
      cout<<"First Stack Size ="<<index1<<endl;
  }
  void SizeOfStack2()
  {
      cout<<"Second Stack Size ="<<index2<<endl;
  }
  bool empty1()
  {
      return (size1 == -1);
  }
  bool empty2()
  {
      return (size1 == ArraySize);
  }
  int top1()
  {
      return (array[size1]);
  }
  int top2()
  {
      return (array[size2]);
  }
  void printStack1()
  {
      cout<<"Printing First Stack Elements"<<endl;
      for(int i =0;i<index1;i++)
      {
          cout<<array[i]<<" ";
      }
      cout<<endl;
  }
  void printStack2()
  {
      cout<<"Printing second Stack Elements"<<endl;
      for(int i = ArraySize-1;i>index2;i--)
      {
          cout<<array[i]<<" ";
      }
      cout<<endl;
  }
};

int main() {
    MyStack st(10);
    st.push1(1);
    st.push1(2);
    st.push1(3);
    st.push1(4);
    st.push1(5);
    st.push2(6);
    st.push2(7);
    st.push2(8);
    st.push2(9);
    st.push2(10);
    st.printStack1();
    st.printStack2();
    st.SizeOfStack1();
    st.SizeOfStack2();
    
    st.pop1();
    st.pop2();
    st.printStack1();
    st.printStack2();
    st.SizeOfStack1();
    st.SizeOfStack2();
    
    st.pop1();
    st.pop2();
    st.printStack1();
    st.printStack2();
    st.printStack1();
    st.printStack2();
    return 0;
}

3. Design a stack that support getMin() in O(1) time and O(1) extra space






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