Add PriorityQueue data structure

.githooks/pre-commit

@@ -0,0 +1,7 @@
+#!/bin/sh
+# Automatically bump patch version before each commit
+
+npm version patch --no-git-tag-version > /dev/null
+
+# stage version files
+git add package.json package-lock.json

DEVELOPMENT_PLAN.md

@@ -17,7 +17,7 @@ This document outlines possible improvements and future developments for the `TS
 ## New Data Structures
 
 - **Graph**: Implement a basic graph structure with common algorithms such as BFS, DFS, and shortest path algorithms.
-- **PriorityQueue**: Provide a priority queue implementation for efficient task scheduling.
+- **PriorityQueue**: Provide a priority queue implementation for efficient task scheduling. *(Implemented)*
 - **Balanced Trees**: Add self-balancing tree variants (e.g., AVL or Red-Black trees) for more efficient search and insert operations.
 
 ## Documentation

README.md

@@ -244,6 +244,44 @@ queue.size(); // 2
 
 ```
 
+## PriorityQueue<T>
+
+#### push(value: T, priority: number)
+
+Insert an element into the queue with an associated priority.
+
+#### pop(): T | null
+
+Removes and returns the element with the highest priority, or `null` if the queue is empty.
+
+#### peek(): T | null
+
+Returns the element with the highest priority without removing it, or `null` if the queue is empty.
+
+#### size(): number
+
+Returns the number of elements in the queue.
+
+#### isEmpty(): boolean
+
+Returns `true` if the queue has no elements, otherwise `false`.
+
+#### toArray(): T[]
+
+Returns an array of the values in priority order.
+
+```typescript
+
+const pq = new PriorityQueue<number>();
+pq.push(5, 5);
+pq.push(1, 1);
+pq.push(3, 3);
+pq.pop(); // 1
+pq.peek(); // 3
+pq.size(); // 2
+
+```
+
 ## BinaryTree<T>
 
 #### getRoot(): BinaryTreeNode<T>
@@ -422,3 +460,13 @@ Traverse the tree in breadth-first order and apply the given callback function t
 
 
 If you have an advice, please feel free to contact with me
+
+## Git Hooks
+
+This project uses a pre-commit hook stored in `.githooks/pre-commit` to
+automatically bump the package patch version each time you commit. Enable the
+hooks with the following command:
+
+```bash
+git config core.hooksPath .githooks
+```

package.json

@@ -1,6 +1,6 @@
 {
   "name": "datastructure-ts",
-  "version": "0.1.20",
+  "version": "0.1.21",
   "description": "Collection of data structures(LinkedList, DoubleLinkedList, Stack, Queue, Dictionary and etc...) for TypeScript.",
   "scripts": {
     "build": "tsc",

src/PriorityQueue/PriorityQueue.ts

@@ -0,0 +1,93 @@
+export interface PriorityQueueItem<T> {
+    value: T;
+    priority: number;
+}
+
+export class PriorityQueue<T> {
+    private heap: PriorityQueueItem<T>[] = [];
+
+    constructor(private compare: (a: number, b: number) => boolean = (a, b) => a < b) {}
+
+    push(value: T, priority: number): void {
+        this.heap.push({ value, priority });
+        this.bubbleUp(this.heap.length - 1);
+    }
+
+    pop(): T | null {
+        if (this.isEmpty()) {
+            return null;
+        }
+        const top = this.heap[0].value;
+        const end = this.heap.pop()!;
+        if (!this.isEmpty()) {
+            this.heap[0] = end;
+            this.bubbleDown(0);
+        }
+        return top;
+    }
+
+    peek(): T | null {
+        return this.isEmpty() ? null : this.heap[0].value;
+    }
+
+    size(): number {
+        return this.heap.length;
+    }
+
+    isEmpty(): boolean {
+        return this.heap.length === 0;
+    }
+
+    toArray(): T[] {
+        return this.heap.map(item => item.value);
+    }
+
+    private bubbleUp(index: number): void {
+        const element = this.heap[index];
+        while (index > 0) {
+            const parentIndex = Math.floor((index - 1) / 2);
+            const parent = this.heap[parentIndex];
+            if (this.compare(element.priority, parent.priority)) {
+                this.heap[parentIndex] = element;
+                this.heap[index] = parent;
+                index = parentIndex;
+            } else {
+                break;
+            }
+        }
+    }
+
+    private bubbleDown(index: number): void {
+        const length = this.heap.length;
+        const element = this.heap[index];
+        while (true) {
+            const leftChildIdx = 2 * index + 1;
+            const rightChildIdx = 2 * index + 2;
+            let swapIdx: number | null = null;
+
+            if (leftChildIdx < length) {
+                const left = this.heap[leftChildIdx];
+                if (this.compare(left.priority, element.priority)) {
+                    swapIdx = leftChildIdx;
+                }
+            }
+
+            if (rightChildIdx < length) {
+                const right = this.heap[rightChildIdx];
+                if (
+                    (swapIdx === null && this.compare(right.priority, element.priority)) ||
+                    (swapIdx !== null && this.compare(right.priority, this.heap[swapIdx].priority))
+                ) {
+                    swapIdx = rightChildIdx;
+                }
+            }
+
+            if (swapIdx === null) {
+                break;
+            }
+            this.heap[index] = this.heap[swapIdx];
+            this.heap[swapIdx] = element;
+            index = swapIdx;
+        }
+    }
+}

src/index.ts

@@ -9,5 +9,6 @@ export * from './Nodes/DoubleLinkedNode';
 export * from './Nodes/LinkedNode';
 export * from './Stack/Stack';
 export * from './Queue/Queue';
+export * from './PriorityQueue/PriorityQueue';
 export * from './Nodes/BinaryTreeNode';
 export * from './BinaryTree/BinaryTree';

tests/PriorityQueue/PriorityQueue.spec.ts

@@ -0,0 +1,34 @@
+import { PriorityQueue } from '../../src/PriorityQueue/PriorityQueue';
+import { expect } from 'chai';
+
+describe('PriorityQueue', () => {
+    let queue: PriorityQueue<string>;
+
+    beforeEach(() => {
+        queue = new PriorityQueue<string>();
+    });
+
+    it('push/pop works according to priority', () => {
+        queue.push('low', 5);
+        queue.push('high', 1);
+        queue.push('medium', 3);
+
+        expect(queue.pop()).equal('high');
+        expect(queue.pop()).equal('medium');
+        expect(queue.pop()).equal('low');
+    });
+
+    it('peek returns highest priority', () => {
+        queue.push('a', 2);
+        queue.push('b', 1);
+
+        expect(queue.peek()).equal('b');
+        expect(queue.size()).equal(2);
+    });
+
+    it('handles empty queue', () => {
+        expect(queue.pop()).equal(null);
+        expect(queue.peek()).equal(null);
+        expect(queue.size()).equal(0);
+    });
+});