Added priority queue

RashikAnsar · RashikAnsar · commit da56f1ad4ac9 · 2018-10-25T09:23:01.000+05:30
diff --git a/data-structures/priorityQueue.js b/data-structures/priorityQueue.js
@@ -0,0 +1,117 @@
+/**
+ * @author Rashik Ansar
+ *
+ * Implemntaion of priority queue
+ * Lower the priority value higher its priority
+ * under the hood its implementing minBinaryHeap
+ */
+class PriorityQueue {
+  constructor() {
+    this.values = [];
+  }
+
+  /**
+   * Adding data to the queue
+   * @param {*} data Data to add into queue
+   * @param {*} priority Priority of the data
+   * @returns {PriorityQueue}
+   */
+  enqueue(data, priority) {
+    let temp = new Node(data, priority);
+    this.values.push(temp);
+    this.bubbleUp();
+    return this;
+  }
+
+  /**
+   * removing a node from the queue
+   * @returns {Node}
+   */
+  dequeue() {
+    const min = this.values[0];
+    const end = this.values.pop();
+    if (this.values.length > 0) {
+      this.values[0] = end;
+      this.sinkDown();
+    }
+    return min;
+  }
+
+  /**
+   * enqueue helper function
+   */
+  bubbleUp() {
+    let index = this.values.length - 1;
+    const element = this.values[index];
+    while (index > 0) {
+      let parentIndex = Math.floor((index - 1) / 2);
+      let parent = this.values[parentIndex];
+      // if (element.priority <= parent.priority) break; //maxBinaryHeap condition
+      if (element.priority >= parent.priority) break; //minBinaryHeap condition
+      this.values[parentIndex] = element;
+      this.values[index] = parent;
+      index = parentIndex;
+    }
+  }
+
+  /**
+   * dequeue helper function
+   */
+  sinkDown() {
+    let index = 0;
+    const length = this.values.length;
+    const element = this.values[index];
+    while (true) {
+      let leftChildIndex = 2 * index + 1;
+      let rightChildIndex = 2 * index + 2;
+      let leftChild;
+      let rightChild;
+      let swap = null;
+
+      if (leftChildIndex < length) {
+        leftChild = this.values[leftChildIndex];
+        // Change below comparision operators to make maxBinaryHeap
+        if (leftChild.priority < element.priority) {
+          swap = leftChildIndex;
+        }
+      }
+
+      if (rightChildIndex < length) {
+        rightChild = this.values[rightChildIndex];
+        // Change below comparision operators to make maxBinaryHeap
+        if (
+          (!swap && rightChild.priority < element.priority) ||
+          (swap && rightChild.priority < leftChild.priority)
+        ) {
+          swap = rightChildIndex;
+        }
+      }
+
+      if (!swap) break;
+
+      this.values[index] = this.values[swap];
+      this.values[swap] = element;
+      index = swap;
+    }
+  }
+}
+
+class Node {
+  constructor(data, priority) {
+    this.data = data;
+    this.priority = priority;
+  }
+}
+
+let a = new PriorityQueue();
+a.enqueue('Common Cold', 10);
+a.enqueue('Gunshot wound', 2);
+a.enqueue('Fever', 8);
+
+console.log(a);
+a.dequeue();
+console.log(a);
+a.dequeue();
+console.log(a);
+a.dequeue();
+console.log(a);
