added implemenation of stacks using queues

Author: mdfaizanahmed786

Stacks/Implementation/ImplementUsingQueues.cpp

@@ -0,0 +1,67 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int main() {
+// usign two queues
+  // of course we can use here queue in class implementation
+  queue<int> q1;
+  queue<int> q2;
+  int i=0;
+  int num;
+  while(i<5){
+  cout<<"Enter a number to insert into stack"<<endl;
+  cin>>num;
+    // algo:
+    // 1. Push element to q2
+    // 2. add element by element to q2 until q1 is not empty
+    // 3. swap q1 and q2
+  q2.push(num);
+  while(!q1.empty()){
+    q2.push(q1.front());
+    q1.pop();
+  }
+   swap(q1, q2);
+  i++;
+
+  }
+
+  
+  while(!q1.empty()){
+    cout<<q1.front()<<" ";
+    q1.pop();
+  }
+
+  // TC: O(N)
+  //  SC:O(2N)
+
+
+  // Optimization of above approach TCO(N) SC:O(2N)
+//   Just go on insert from bottom to the top in queue 
+queue<int> q3;
+int j=0;
+  while(j<5){
+    cout<<"Enter the number that you want to insert into the stack:"<<endl;
+    int x;
+    cin>>x;
+    q3.push(x);
+    for(int i=0; i<q3.size()-1; i++){
+      q3.push(q3.front());
+      q3.pop();
+    }
+
+    j++;
+    
+  }
+
+
+  while(!q3.empty()){
+    cout<<q3.front()<<" ";
+    q3.pop();
+  }
+  
+  
+
+  
+  
+  
+}