Add day 44

Author: MadhavBahl

README.md

@@ -71,6 +71,7 @@ Motivate yourself to code daily till 60 days, and see the magic! Coding will bec
 | [Day 41](./day41) | [Implement Queue Data Structure](./day41) | [http://codetoexpress.tech/dc/day41/](http://codetoexpress.tech/dc/day41/) | **Beginner** |
 | [Day 42](./day42) | [Alternate Queue Combination](./day42) | [http://codetoexpress.tech/dc/day42/](http://codetoexpress.tech/dc/day42/) | **intermediate** |
 | [Day 43](./day43) | [Queue Reversal](./day43) | [http://codetoexpress.tech/dc/day43/](http://codetoexpress.tech/dc/day43/) | **intermediate** |
+| [Day 44](./day44) | [Queue from Stacks](./day44) | [http://codetoexpress.tech/dc/day44/](http://codetoexpress.tech/dc/day44/) | **intermediate** |
 
 ## [More Problems](./BONUS/README.md)
 

day44/JavaScript/queueFromStack.js

@@ -0,0 +1,79 @@
+/**
+ * Queue from stack 
+ */
+
+// Class declaration for queue data structure
+class Queue {
+    constructor(size) {
+        this.first = new Stack();
+        this.second = new Stack();
+    }
+
+    enqueue(element) {
+        this.first.push(element);
+    }
+
+    dequeue() {
+        // Empty first stack to second
+        while (this.first.peek()) {
+            this.second.push(this.first.pop());
+        }
+
+        const element = this.second.pop();
+
+        // Restore first stack
+        while (this.second.peek()) {
+            this.first.push(this.second.pop());
+        }
+
+        return element;
+    }
+
+    peek() {
+        while (this.first.peek()) {
+            this.second.push(this.first.pop());
+        }
+
+        const element = this.second.peek();
+
+        while (this.second.peek()) {
+            this.first.push(this.second.pop());
+        }
+
+        return element;
+    }
+}
+
+// Class declaration for stack data structure
+class Stack {
+    constructor() {
+        this.data = [];
+    }
+
+    push(record) {
+        this.data.push(record);
+    }
+
+    pop() {
+        return this.data.pop();
+    }
+
+    peek() {
+        return this.data[this.data.length - 1];
+    }
+}
+
+const q = new Queue();
+
+q.enqueue(1);
+console.log(q.dequeue());
+q.enqueue(1);
+q.enqueue(2);
+q.enqueue(3);
+console.log(q.dequeue());
+console.log(q.dequeue());
+console.log(q.dequeue());
+q.enqueue(1);
+q.enqueue(2);
+console.log(q.peek());
+console.log(q.peek());

day44/README.md

@@ -0,0 +1,66 @@
+![cover](./cover.png)
+
+# Day 44 - Queue from Stacks
+
+Implement the Queue data structure using Stacks
+
+### Hint
+
+Use 2 stacks
+
+- enqueue operation same as push in a single stack
+- For dequeue, pop all the elements of first stack into second and apply pop once in second queue
+- for peek, again, pop all the elements of first stack into second and apply peek once in second queue
+
+Don't forget to restore the state of first stack after the dequeue and peek operations
+
+## Solution
+
+## JavaScript Implementation
+
+### [Solution](./JavaScript/queueFromStack.js)
+
+```js
+class Queue {
+    constructor(size) {
+        this.first = new Stack();
+        this.second = new Stack();
+    }
+
+    enqueue(element) {
+        this.first.push(element);
+    }
+
+    dequeue() {
+        // Empty first stack to second
+        while (this.first.peek()) {
+            this.second.push(this.first.pop());
+        }
+
+        const element = this.second.pop();
+
+        // Restore first stack
+        while (this.second.peek()) {
+            this.first.push(this.second.pop());
+        }
+
+        return element;
+    }
+
+    peek() {
+        while (this.first.peek()) {
+            this.second.push(this.first.pop());
+        }
+
+        const element = this.second.peek();
+
+        while (this.second.peek()) {
+            this.first.push(this.second.pop());
+        }
+
+        return element;
+    }
+}
+```
+
+[Click Here](./JavaScript/queueFromStack.js) for complete solution