Create StackusingQueue.java

deepukumar18 · web-flow · commit aef99c015453 · 2020-10-01T15:51:57.000+05:30
diff --git a/StackusingQueue.java b/StackusingQueue.java
@@ -0,0 +1,82 @@
+/* Java Program to implement a stack using 
+two queue */
+import java.util.*; 
+
+class GfG { 
+
+	static class Stack { 
+		// Two inbuilt queues 
+		static Queue<Integer> q1 = new LinkedList<Integer>(); 
+		static Queue<Integer> q2 = new LinkedList<Integer>(); 
+
+		// To maintain current number of 
+		// elements 
+		static int curr_size; 
+
+		Stack() 
+		{ 
+			curr_size = 0; 
+		} 
+
+		static void push(int x) 
+		{ 
+			curr_size++; 
+
+			// Push x first in empty q2 
+			q2.add(x); 
+
+			// Push all the remaining 
+			// elements in q1 to q2. 
+			while (!q1.isEmpty()) { 
+				q2.add(q1.peek()); 
+				q1.remove(); 
+			} 
+
+			// swap the names of two queues 
+			Queue<Integer> q = q1; 
+			q1 = q2; 
+			q2 = q; 
+		} 
+
+		static void pop() 
+		{ 
+
+			// if no elements are there in q1 
+			if (q1.isEmpty()) 
+				return; 
+			q1.remove(); 
+			curr_size--; 
+		} 
+
+		static int top() 
+		{ 
+			if (q1.isEmpty()) 
+				return -1; 
+			return q1.peek(); 
+		} 
+
+		static int size() 
+		{ 
+			return curr_size; 
+		} 
+	} 
+
+	// driver code 
+	public static void main(String[] args) 
+	{ 
+		Stack s = new Stack(); 
+		s.push(1); 
+		s.push(2); 
+		s.push(3); 
+
+		System.out.println("current size: " + s.size()); 
+		System.out.println(s.top()); 
+		s.pop(); 
+		System.out.println(s.top()); 
+		s.pop(); 
+		System.out.println(s.top()); 
+
+		System.out.println("current size: " + s.size()); 
+	} 
+} 
+// This code is contributed by Prerna 
