feat: stack implementation with array

src/stack/README.md

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+# 栈
+
+栈(stack)，也称堆栈，在计算机科学领域中，栈是一种线性数据结构，它只能在数据串列或阵列的一端进行入栈(push)和出栈(pop)操作，按照后进先出(LIFO)原理进行运作

src/stack/__tests__/index.ts

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+import { Stack } from '../index'
+
+describe('Stack', () => {
+  let stack: Stack
+
+  beforeEach(() => {
+    stack = new Stack()
+  })
+
+  it('should create a empty Stack', () => {
+    const stack: Stack = new Stack()
+    expect(stack).toBeDefined()
+    expect(stack).toBeInstanceOf(Stack)
+    expect(stack.toString()).toBe('')
+  })
+
+  it('shoule push value', () => {
+    /** */
+    stack.push(1)
+    expect(stack.toString()).toBe('1')
+    stack.push(1)
+    expect(stack.toString()).toBe('1,1')
+  })
+
+  it('shoule pop value', () => {
+    stack.push(1)
+    expect(stack.toString()).toBe('1')
+    stack.pop()
+    expect(stack.toString()).toBe('')
+  })
+
+  it('shoule push/pop value in LIFO order', () => {
+    stack.push(1)
+    stack.push(2)
+    stack.push(3)
+    expect(stack.toString()).toBe('1,2,3')
+    expect(stack.pop()).toBe(3)
+    expect(stack.toString()).toBe('1,2')
+    expect(stack.pop()).toBe(2)
+    expect(stack.toString()).toBe('1')
+    expect(stack.pop()).toBe(1)
+    expect(stack.toString()).toBe('')
+  })
+
+  it('shoule return isEmpty', () => {
+    expect(stack.isEmpty()).toBeTruthy()
+    stack.push(1)
+    expect(stack.isEmpty()).toBeFalsy()
+    stack.push(2)
+    expect(stack.isEmpty()).toBeFalsy()
+    stack.pop()
+    stack.pop()
+    expect(stack.isEmpty()).toBeTruthy()
+  })
+
+  it('shoule set size correctly', () => {
+    expect(stack.size).toBe(0)
+    stack.push(1)
+    expect(stack.size).toBe(1)
+    stack.push(1)
+    expect(stack.size).toBe(2)
+    stack.pop()
+    stack.pop()
+    expect(stack.size).toBe(0)
+  })
+
+  it('shoule return null when list is empty', () => {
+    expect(stack.isEmpty()).toBeTruthy()
+    expect(stack.pop()).toBe(null)
+  })
+})

src/stack/index.ts

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+/**
+ * 栈的数组实现
+ */
+
+export class Stack {
+  private list: any[]
+
+  constructor() {
+    this.list = []
+  }
+
+  public get size() {
+    return this.list.length
+  }
+
+  public push(item: any) {
+    this.list.push(item)
+  }
+
+  public pop() {
+    if (this.list.length === 0) {
+      return null
+    }
+    return this.list.pop()
+  }
+
+  public isEmpty(): boolean {
+    return this.list.length === 0
+  }
+
+  public toString(): string {
+    return this.list.toString()
+  }
+}