feat(queue): queue implementation

src/queue/README.md

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+# 队列
+
+在计算机科学中, 一个 **队列(queue)** 是一种特殊类型的抽象数据类型或集合。集合中的实体按顺序保存。
+
+队列基本操作有两种: 向队列的后端位置添加实体，称为入队，并从队列的前端位置移除实体，称为出队。
+
+队列中元素先进先出 FIFO (first in, first out)

src/queue/__tests__/index.ts

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+import { Queue } from '../index'
+
+describe("Queue", () => {
+  it("should create an empty queue", () => {
+    const queue = new Queue();
+    expect(queue).not.toBeNull();
+    expect(queue.length).toBe(0);
+  })
+
+  it("should enqueue data to queue", () => {
+    const queue = new Queue()
+    queue.enqueue(1)
+    queue.enqueue(2)
+    expect(queue.toString()).toBe('1,2')
+  })
+
+  it("should have length for queue correctly", () => {
+    const queue = new Queue();
+    expect(queue.length).toBe(0);
+    queue.enqueue(1)
+    queue.enqueue(2)
+    expect(queue.length).toBe(2);
+  })
+
+  it("should dequeue from queue in FIFO order", () => {
+    const queue = new Queue()
+    queue.enqueue(1)
+    queue.enqueue(2)
+
+    expect(queue.dequeue()).toBe(1);
+    expect(queue.length).toBe(1)
+    expect(queue.toString()).toBe('2')
+
+    expect(queue.dequeue()).toBe(2);
+    expect(queue.length).toBe(0)
+    expect(queue.toString()).toBe('')
+  })
+
+  it("should enqueue/dequeue any data to/from queue", () => {
+    const queue = new Queue()
+
+    const valueTest = [
+      {a: "test", b: 123},
+      [],
+      () => {/** */}
+    ]
+
+    valueTest.forEach((item) => {
+      queue.enqueue(item)
+    })
+
+    expect(queue.length).toBe(valueTest.length)
+    expect(queue.toString()).toEqual(valueTest.toString())
+
+    valueTest.forEach((item) => {
+      queue.dequeue()
+    })
+
+    expect(queue.length).toBe(0)
+    expect(queue.toString()).toEqual('')
+  })
+
+  it("should return isEmpty for queue", () => {
+    const queue = new Queue();
+    expect(queue.isEmpty()).toBeTruthy();
+    queue.enqueue(1)
+    queue.enqueue(2)
+    expect(queue.isEmpty()).toBeFalsy()
+  })
+
+  it("should return length for queue correctly", () => {
+    const queue = new Queue();
+    expect(queue.isEmpty()).toBeTruthy();
+    queue.enqueue(1)
+    queue.enqueue(2)
+    expect(queue.isEmpty()).toBeFalsy()
+  })
+
+  it("should peek item from queue", () => {
+    const queue = new Queue();
+
+    expect(queue.peek()).toBe(null);
+
+    queue.enqueue(1)
+    queue.enqueue(2)
+
+    expect(queue.peek()).toBe(1);
+    expect(queue.peek()).toBe(1);
+
+    queue.dequeue()
+
+    expect(queue.peek()).toBe(2);
+
+    queue.dequeue()
+
+    expect(queue.peek()).toBe(null);
+    expect(queue.peek()).toBe(null);
+  })
+})

src/queue/index.ts

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+/**
+ * 数组版本的队列
+ */
+
+export class Queue {
+  private list: any[] = [];
+
+  constructor() {
+    this.list = [];
+  }
+
+  get length() {
+    return this.list.length;
+  }
+
+  isEmpty() {
+    return this.list.length === 0;
+  }
+
+  enqueue(item: any) {
+    this.list.push(item);
+  }
+
+  dequeue() {
+    if(this.list.length === 0) {
+      return null;
+    }
+    return this.list.shift();
+  }
+
+  /**
+   * 查看首个节点
+   */
+  peek() {
+    return this.list.length > 0 ? this.list[0] : null;
+  }
+
+  toString() {
+    return this.list.toString();
+  }
+}