Added a folder Queue Using Stacks and two programs - Queue Using Stac…

Queue Using Stacks/Queue Using Stacks - Costly Dequeue.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+struct Queue {
+    stack<int> s1, s2;
+
+    void enQueue(int x)
+    {
+        s1.push(x);
+    }
+
+    int deQueue()
+    {
+        if (s1.empty() && s2.empty()) {
+            cout << "Q is empty";
+            exit(0);
+        }
+
+        if (s2.empty()) {
+            while (!s1.empty()) {
+                s2.push(s1.top());
+                s1.pop();
+            }
+        }
+
+        int x = s2.top();
+        s2.pop();
+        return x;
+    }
+};
+
+int main()
+{
+    Queue q;
+    q.enQueue(1);
+    q.enQueue(2);
+    q.enQueue(3);
+
+    cout << q.deQueue() << '\n';
+    cout << q.deQueue() << '\n';
+    cout << q.deQueue() << '\n';
+
+    return 0;
+}

Queue Using Stacks/Queue Using Stacks - Costly Enqueue.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+struct Queue {
+    stack<int> s1, s2;
+
+    void enQueue(int x)
+    {
+        while (!s1.empty()) {
+            s2.push(s1.top());
+            s1.pop();
+        }
+
+        s1.push(x);
+
+        while (!s2.empty()) {
+            s1.push(s2.top());
+            s2.pop();
+        }
+    }
+
+    int deQueue()
+    {
+        if (s1.empty()) {
+            cout << "Q is Empty";
+            exit(0);
+        }
+
+        int x = s1.top();
+        s1.pop();
+        return x;
+    }
+};
+
+int main()
+{
+    Queue q;
+    q.enQueue(1);
+    q.enQueue(2);
+    q.enQueue(3);
+
+    cout << q.deQueue() << '\n';
+    cout << q.deQueue() << '\n';
+    cout << q.deQueue() << '\n';
+
+    return 0;
+}