Live Note

Remain optimistic

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并查集

用集合中的某个元素来代表这个集合，该元素称为集合的代表元。
一个集合内的所有元素组织成以代表元为根的树形结构。
对于每一个元素parent[x]指向 x 在树形结构上的父亲节点。如果 x 是根节点，则令parent[x] = x。
对于查找操作，假设需要确定 x 所在的的集合，也就是确定集合的代表元。可以沿着parent[x]不断在树形结构中向上移动，直到到达根节点。

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广度优先搜索

在 N * M 的网格中，从 start 走到 end 。
广度解法：需要一个队列，从 start 节点开始，当一个节点抛出时，将它周围的节点入队，直至抛出的节点是 end 节点。
模拟网格：

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var map = [
  // map[x][y]
  [0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0],
  [0, 0, 1, 0, 0, 0],
  [0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 2],
]
find(map)
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HTML 框架

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<style>
  #box {
    width: 300px;
    height: 300px;
    background-color: #ddd;
  }
  #child {
    width: 200px;
    height: 100px;
    background-color: orange;
  }
</style>
<div id="box">
  <div id="child">target</div>
</div>
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同源策略

  • 同源策略（MDN 解释）：限制从一个源加载的文档或脚本如何与来自另一个源的资源进行交互。这是一个用于隔离潜在恶意文件的关键的安全机制。
  • 源：协议、域名、端口。
  • 限制：无法获取 Cookie 、 LocalStorage 和 IndexDB ，无法操作 dom ，不能发送 Ajax 。
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.gitignore 文件的配置

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# Numerous always-ignore extensions

_.bak
_.patch
_.diff
_.err

# temp file for git conflict merging

_.orig
_.log
_.rej
_.swo
_.swp
_.zip
_.vi
_~
_.sass-cache
_.tmp.html
\*.dump

# OS or Editor folders

.DS*Store
.*_
.cache
.project
.settings
.tmproj
_.esproj
_.sublime-project
_.sublime-workspace
nbproject
thumbs.db
\*.iml

# Folders to ignore

.hg
.svn
.CVS
.idea
node_modules/
jscoverage_lib/
bower_components/
dist/

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class Node {
  constructor(data = -1, prev = null, next = null) {
    this.data = data
    this.prev = prev // 向前指针
    this.next = next // 向后指针
  }
}

class LinkList {
  constructor() {
    this.head = this.tail = null // 首、尾指针
    this.size = 0 // 元素个数
  }

  addHead(elem) {
    let elemNode = new Node(elem)
    if (this.size == 0) {
      this.head = this.tail = elemNode
      this.size++
    } else {
      this.head.prev = elemNode
      elemNode.next = this.head
      this.head = elemNode
      this.size++
    }
    return true
  }

  deleteHead() {
    if (this.size != 0) {
      let elem = this.head.data
      this.head.prev = null
      this.head = this.head.next
      this.size--
      return elem
    } else {
      console.log("list is empty")
      return
    }
  }

  addTail(elem) {
    let elemNode = new Node(elem)
    if (this.size == 0) {
      this.head = this.tail = elemNode
      this.size++
    } else {
      elemNode.prev = this.tail
      this.tail.next = elemNode
      this.tail = elemNode
      this.size++
    }
    return true
  }

  deleteTail() {
    if (this.size != 0) {
      let elem = this.tail.data
      this.tail.next = null
      this.tail = this.tail.prev
      this.size--
      return elem
    } else {
      console.log("list is empty")
      return
    }
  }

  display() {
    let current = this.head,
      count = this.size,
      str = ""
    while (count > 0) {
      str += current.data + " "
      current = current.next
      count--
    }
    console.log(str)
  }
}
let linklist = new LinkList()
linklist.addHead(1)
linklist.addHead(2)
linklist.addHead(3)
linklist.deleteHead()
linklist.addTail(4)
linklist.display()

结果

2 1 4

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简单的 Queue 实现

数组实现

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class Queue {
  constructor(size = 10) {
    this.size = size // 队列最大长度
    this.top = 0 // 首位置
    this.bottom = -1 // 尾位置
    this.elems = 0 // 成员个数
    this.arr = [] // 队列
  }

  add(elem) {
    if (this.elems == this.size) {
      console.log("Queue is full")
      return
    }
    if (this.bottom == this.size - 1) {
      // 循环队列
      this.bottom = -1
    }
    this.arr[++this.bottom] = elem
    this.elems++
    return true
  }

  out() {
    if (this.elems == 0) {
      console.log("Queue is empty")
      return
    }
    let elem = this.arr[this.top]
    this.arr[this.top] = null
    this.top++
    if (this.top == this.size) {
      this.top = 0
    }
    this.elems--
    return elem
  }
}
var queue = new Queue()
queue.add(3)
queue.add(2)
console.log(queue.out())
console.log(queue.out())
console.log(queue.out())
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简单的 Stack 实现

数组实现

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class Stack {
  constructor(size = 10) {
    this.arr = [] // 栈
    this.size = size // 最大长度
    this.top = -1 // 栈顶
  }

  push(elem) {
    if (this.top == this.size) {
      this.size *= 2
    }
    this.arr[++this.top] = elem
    return true
  }

  pop() {
    let elem = this.arr[this.top--]
    return elem
  }

  peekTop() {
    if (this.top == -1) {
      console.log("stack is empty")
      return
    }
    return this.arr[this.top]
  }

  print() {
    let str = ""
    for (let i = 0; i <= this.top; i++) {
      str += this.arr[i] + " "
    }
    console.log(str)
  }
}
var stack = new Stack()
stack.push(1)
stack.push(2)
stack.pop()
console.log(stack.peekTop())
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简单的 Array 实现

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class Array {
  constructor(size = 10) {
    this.arr = [] // 数组
    this.size = size // 最大长度
    this.elems = 0 // 成员数量
  }

  add(elem) {
    if (this.arr.length == this.size) {
      console.log("Array is full")
      return
    }
    this.arr[this.elems++] = elem
    return true
  }

  find(elem) {
    for (let i = 0, len = this.elems; i < len; i++) {
      if (this.arr[i] == elem) return i
    }
    return -1
  }

  delete(elem) {
    let index = this.find(elem)
    if (index == -1) {
      console.log("Element not found")
      return
    }
    for (let i = index, len = this.elems - 1; i < len; i++)
      this.arr[i] = this.arr[i + 1]
    this.elems--
    return true
  }

  update(oldVal, newVal) {
    // only use for unique element
    let index = this.find(oldVal)
    if (index == -1) {
      console.log("Element not found")
      return
    }
    this.arr[index] = newVal
    return true
  }

  display() {
    let srt = ""
    for (let i = 0, len = this.elems; i < len; i++) {
      srt += "" + this.arr[i] + " "
    }
    console.log(srt)
  }

  length() {
    return this.elems
  }
}
var arr = new Array()
arr.add(1)
arr.add(2)
arr.add(3)
arr.add(4)
arr.display()
console.log(arr.length())

结果

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** 需求：已知一个路径，读取文件内容并返回 **

  • 普通读取文件方式：
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const fs = require("fs")
const path = require("path")
fs.readFile(path.join(__dirname, "./1.txt"), "utf-8", (err, dataStr) => {
  if (err) throw err
  console.log(dataStr)
})
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