adding some more problems like implementing stack using queue

ch1/19_Stack/main.cpp

@@ -18,4 +18,100 @@ int main() {
         else if (!stack.isEmpty()) cout << stack.pop() << " ";
     }
     cout << "(" << stack.size() << " left on stack)" << endl;
-}
+}
+// adding some more problems like implementing stack using queue
+/* Program to implement a stack  
+using two queue */
+#include <bits/stdc++.h> 
+using namespace std; 
+
+class Stack { 
+    queue<int> q1, q2; 
+    int curr_size; 
+
+public: 
+    Stack() 
+    { 
+        curr_size = 0; 
+    } 
+
+    void pop() 
+    { 
+        if (q1.empty()) 
+            return; 
+
+        // Leave one element in q1 and 
+        // push others in q2. 
+        while (q1.size() != 1) { 
+            q2.push(q1.front()); 
+            q1.pop(); 
+        } 
+
+        // Pop the only left element 
+        // from q1 
+        q1.pop(); 
+        curr_size--; 
+
+        // swap the names of two queues 
+        queue<int> q = q1; 
+        q1 = q2; 
+        q2 = q; 
+    } 
+
+    void push(int x) 
+    { 
+        q1.push(x); 
+        curr_size++; 
+    } 
+
+    int top() 
+    { 
+        if (q1.empty()) 
+            return -1; 
+
+        while (q1.size() != 1) { 
+            q2.push(q1.front()); 
+            q1.pop(); 
+        } 
+
+        // last pushed element 
+        int temp = q1.front(); 
+
+
+        q1.pop(); 
+
+        q2.push(temp); 
+
+        // swap the two queues names 
+        queue<int> q = q1; 
+        q1 = q2; 
+        q2 = q; 
+        return temp; 
+    } 
+
+    int size() 
+    { 
+        return curr_size; 
+    } 
+}; 
+
+
+int main() 
+{ 
+    Stack s; 
+    s.push(1); 
+    s.push(2); 
+    s.push(3); 
+    s.push(4); 
+
+    cout << "current size: " << s.size() 
+         << endl; 
+    cout << s.top() << endl; 
+    s.pop(); 
+    cout << s.top() << endl; 
+    s.pop(); 
+    cout << s.top() << endl; 
+    cout << "current size: " << s.size() 
+         << endl; 
+    return 0; 
+}