Add day42

Author: MadhavBahl

README.md

@@ -69,6 +69,7 @@ Motivate yourself to code daily till 60 days, and see the magic! Coding will bec
 | [Day 39](./day39) | [Maximum Element and Reverse Stack](./day39) | [http://codetoexpress.tech/dc/day39/](http://codetoexpress.tech/dc/day39/) | **Intermediate** |
 | [Day 40](./day40) | [Prefix, Infix, Postfix Conversion](./day40) | [http://codetoexpress.tech/dc/day40/](http://codetoexpress.tech/dc/day40/) | **Intermediate** |
 | [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** |
 
 ## [More Problems](./BONUS/README.md)
 

day40/ques.png

@@ -0,0 +1,84 @@
+/**
+ * Alternate Queue Combination
+ * @author MadhavBahlMD
+ * @date 15/02/2019
+ */
+
+class Queue {
+    constructor (size) {
+        this.capacty = size;
+        this.data = [];
+        this.frontIndex = 0;
+        this.rearIndex = 0;
+    }
+
+    front () {
+        return data[this.frontIndex];
+    }
+
+    rear () {
+        return data[this.rearIndex];
+    }
+
+    enqueue (element) {
+        if (this.rearIndex >= this.capacty)  {
+            console.log ("Overflow!");
+            return -1;
+        }
+        this.data.unshift (element);
+        // console.log (element + ' added to the queue');
+        this.rearIndex++;
+    }
+
+    dequeue (element) {
+        if (this.rearIndex === 0) {
+            console.log ("Underflow!");
+            return -1;
+        }
+        // console.log (this.data[this.rearIndex -1] + ' has been removed from the queue');
+        this.rearIndex--;
+        return this.data.pop ();
+    }
+
+    displayQueue () {
+        let toBeDisplayed = '-> ';
+        for (let element of this.data) {
+            toBeDisplayed += element + ' -> ';
+        }
+        console.log (toBeDisplayed);
+    }
+}
+
+const combine = (q1, q2) => {
+    let toBeAdded;
+    const combinedQueue = new Queue (q1.rearIndex + q2.rearIndex);
+    while (!(q1.rearIndex === 0 || q2.rearIndex === 0)) {
+        toBeAdded = q1.dequeue();
+        combinedQueue.enqueue (toBeAdded);
+        toBeAdded = q2.dequeue();
+        combinedQueue.enqueue (toBeAdded);
+    }
+    console.log ("\n/* ===== Displaying Combined Queue ===== */");
+    combinedQueue.displayQueue();
+}
+
+const firstQ = new Queue (4);
+
+firstQ.enqueue (1);
+firstQ.enqueue (2);
+firstQ.enqueue (3);
+firstQ.enqueue (4);
+
+const secondQ = new Queue (4);
+
+secondQ.enqueue (5);
+secondQ.enqueue (6);
+secondQ.enqueue (7);
+secondQ.enqueue (8);
+
+console.log ("\n/* ===== Displaying Queue 1 ===== */");
+firstQ.displayQueue();
+console.log ("\n/* ===== Displaying Queue 2 ===== */");
+secondQ.displayQueue();
+
+combine (firstQ, secondQ);

day41/ques.png

@@ -0,0 +1,112 @@
+![cover](./cover.png)
+
+# Day 42 - Alternate Queue Combination
+
+Given 2 queues, write a function to combine those 2 queues into a single queue such that the elements in the combined queue are from first queue and second queue alternatively
+
+If the lengths of queues are not equal, stop after all elements of the smaller queue are addded to the combined queue
+
+![process](./proc.png)
+
+## Example:
+
+```
+q1  -> 4 -> 3 -> 2 -> 1 ->
+q2  -> 8 -> 7 -> 6 -> 5 ->
+
+combined queue: 
+-> 8 -> 4 -> 7 -> 3 -> 6 -> 2 -> 5 -> 1 ->
+```
+
+![ques](./ques.png)
+
+## Solution
+
+## JavaScript Implementation
+
+### [Solution](./JavaScript/queue.js)
+
+```js
+class Queue {
+    constructor (size) {
+        this.capacty = size;
+        this.data = [];
+        this.frontIndex = 0;
+        this.rearIndex = 0;
+    }
+
+    front () {
+        return data[this.frontIndex];
+    }
+
+    rear () {
+        return data[this.rearIndex];
+    }
+
+    enqueue (element) {
+        if (this.rearIndex >= this.capacty)  {
+            console.log ("Overflow!");
+            return -1;
+        }
+        this.data.unshift (element);
+        // console.log (element + ' added to the queue');
+        this.rearIndex++;
+    }
+
+    dequeue (element) {
+        if (this.rearIndex === 0) {
+            console.log ("Underflow!");
+            return -1;
+        }
+        // console.log (this.data[this.rearIndex -1] + ' has been removed from the queue');
+        this.rearIndex--;
+        return this.data.pop ();
+    }
+
+    displayQueue () {
+        let toBeDisplayed = '-> ';
+        for (let element of this.data) {
+            toBeDisplayed += element + ' -> ';
+        }
+        console.log (toBeDisplayed);
+    }
+}
+
+const combine = (q1, q2) => {
+    let toBeAdded;
+    const combinedQueue = new Queue (q1.rearIndex + q2.rearIndex);
+    while (!(q1.rearIndex === 0 || q2.rearIndex === 0)) {
+        toBeAdded = q1.dequeue();
+        combinedQueue.enqueue (toBeAdded);
+        toBeAdded = q2.dequeue();
+        combinedQueue.enqueue (toBeAdded);
+    }
+    console.log ("\n/* ===== Displaying Combined Queue ===== */");
+    combinedQueue.displayQueue();
+}
+
+const firstQ = new Queue (4);
+
+firstQ.enqueue (1);
+firstQ.enqueue (2);
+firstQ.enqueue (3);
+firstQ.enqueue (4);
+
+const secondQ = new Queue (4);
+
+secondQ.enqueue (5);
+secondQ.enqueue (6);
+secondQ.enqueue (7);
+secondQ.enqueue (8);
+
+console.log ("\n/* ===== Displaying Queue 1 ===== */");
+firstQ.displayQueue();
+console.log ("\n/* ===== Displaying Queue 2 ===== */");
+secondQ.displayQueue();
+
+combine (firstQ, secondQ);
+```
+
+#### Output
+
+![output](./output.png)