Merge pull request matthewsamuel95#287 from dreamerHarshit/new_master

Program to implement queue using stack.

Author: matthewsamuel95

DataStructures/Queue/queue_using_stack.cpp

@@ -0,0 +1,80 @@
+/* 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 push(int x)
+    {
+        curr_size++;
+
+        // Push x first in empty q2
+        q2.push(x);
+
+        // Push all the remaining
+        // elements in q1 to q2.
+        while (!q1.empty())
+        {
+            q2.push(q1.front());
+            q1.pop();
+        }
+
+        // swap the names of two queues
+        queue<int> q = q1;
+        q1 = q2;
+        q2 = q;
+    }
+
+    void pop(){
+
+        // if no elements are there in q1
+        if (q1.empty())
+            return ;
+        q1.pop();
+        curr_size--;
+    }
+
+    int top()
+    {
+        if (q1.empty())
+            return -1;
+        return q1.front();
+    }
+
+    int size()
+    {
+        return curr_size;
+    }
+};
+
+//main function
+int main()
+{
+    Stack stk;
+    stk.push(1);
+    stk.push(2);
+    stk.push(3);
+
+    cout << "current size: " << stk.size()
+         << endl;
+    cout << stk.top() << endl;
+    stk.pop();
+    cout << stk.top() << endl;
+    stk.pop();
+    cout << stk.top() << endl;
+
+    cout << "current size: " << stk.size()
+         << endl;
+    return 0;
+}