Create 04_Create a Priority Queue Class.md

Author: ps0305

Coding Interview Prep/Data Structures/04_Create a Priority Queue Class.md

@@ -0,0 +1,61 @@
+A Priority Queue is a special type of Queue in which items may have additional information which specifies their priority.
+This could be simply represented with an integer.
+Item priority will override placement order in determining the sequence items are dequeued.
+If an item with a higher priority is enqueued after items with lower priority, 
+the higher priority item will be dequeued before all the others.
+
+For instance, let’s imagine we have a priority queue with three items:
+
+`[['kitten', 2], ['dog', 2], ['rabbit', 2]]`
+
+Here the second value (an integer) represents item priority. If we enqueue `['human', 1]` with a priority of `1` (assuming lower priorities are given precedence) it would then be the first item to be dequeued. The collection would like this:
+
+`[['human', 1], ['kitten', 2], ['dog', 2], ['rabbit', 2]]`.
+
+We’ve started writing a `PriorityQueue` in the code editor.
+You will need to add an `enqueue` method for adding items with a priority,
+a `dequeue` method for removing items, a `size` method to return the number of items in the queue,
+a `front` method to return the element at the front of the queue,
+and finally an `isEmpty` method that will return true if the queue is empty or false if it is not.
+
+The enqueue should accept items with the format shown above `(['human', 1])` where `1` represents the priority.
+The dequeue should return only the current item, not its priority.
+
+```js
+function PriorityQueue () {
+    this.collection = [];
+    this.printCollection = function() {
+      console.log(this.collection);
+    };
+    this.enqueue = function(priorityItem) {
+      let inserted = false;
+      for (let i = 0; i < this.collection.length; i++) {
+        let _value = this.collection[i];
+        if (_value[1] > priorityItem[1]) {
+          this.collection.splice(i, 0, priorityItem);
+          inserted = true;
+          break;
+        }
+      }
+      if (!inserted) {
+        this.collection.push(priorityItem);
+      }
+    }
+
+    this.dequeue = function() {
+      let val = this.collection.shift();
+      return val[0]
+    }
+
+    this.size = function() {
+      return this.collection.length;
+    }
+
+    this.isEmpty = function() {
+      return this.collection.length === 0;
+    }
+
+    this.front = function() {
+      return this.collection[0]
+    }  
+}