hjcian / code-practices

code practices (leetcode, codesignal, codewars) by Go, JS, Typescript, Python

個人程式碼練習集中存放區

• Problems & practices
  • Leetcode
  • classic data structures & algorithms practices
  • Codewars
  • CodeSignal
• 類似觀念集中整理
  • Binary search variants
• 基礎知識/DSA
  • algorithms
  • data structures
  • Bitwise operation
    • XOR 特性
    • Brian Kernighan’s Algorithm (count set bits in an integer)
  • Miscellaneous
• 參考資料
  • 練習順序
• Dev environment setup
  • Enable Standard with babel-eslint/parser
• Miscellaneous
  • 指令備忘錄
    • Go
    • folder management
  • 有趣的議題
  • Custom badge
  • Partner

Problems & practices

Leetcode

• 1. Two Sum - go, python
• 20. Valid Parentheses - python
• 26. Remove Duplicates from Sorted Array - go, python
• 27. Remove Element - go, python
• 35. Search Insert position - go
• 53. Maximum Subarray - go, python
• (DP) 70. Climbing Stairs - go
• 88. Merge Sorted Array
• (tree) 94. Binary Tree Inorder Traversal - go (recursive, iterative)
• (tree) 144. Binary Tree Preorder Traversal - go (recursive, iterative)
• ⚠️ (tree) 145. Binary Tree Postorder Traversal - go... iterative 還想不通 😫
• 219. Contains Duplicate II
• 283. Move Zeroes
• 287. Find the Duplicate Number
• 338. Counting Bits
• (DP) 509. Fibonacci Number - go
• 532. K-diff Pairs in an Array
• 561. Array Partition I
• 566. Reshape the Matrix
• 628. Maximum Product of Three Numbers
• 704. BinarySearch
• 746. Min Cost Climbing Stairs👁‍🗨
• 766. Toeplitz Matrix👁‍🗨
• 867. Transpose Matrix
• 977. Squares of a Sorted Array👁‍🗨

• 2. Add Two Numbers
• 3. Longest Substring Without Repeating Characters
• 11. Container With Most Water👁‍🗨
• 15. 3Sum👁‍🗨
• 16. 3Sum Closest👁‍🗨 3-pointers skill
• 19. Remove Nth Node From End of List
• 33. Search in Rotated Sorted Array - python
• 39. Combination Sum 😞👁‍🗨
• 48. Rotate Image👁‍🗨
• 54. Spiral Matrix
• 56. Merge Intervals
• 75. Sort Colors - go
• 1143. Longest Common Subsequence

• 72. Edit Distance
  • related: 1143. Longest Common Subsequence (ref)

classic data structures & algorithms practices

• Sortings
• Bloom Filter - a naive proof of concept
  • 資料結構大便當：Bloom Filter
  • usages: crypto/hash, Go: Convert byte array to big.Int, Go: modulus using math big package, Go: big.Int SetBit()/Bit()

Codewars

• Return substring instance count 2
• Simple Pig Latin
• Pick peaks
• Interlaced Spiral Cipher

CodeSignal

• convertIPv4
• christmasTree
• happyNumber: go, ts
• videoPart: go, ts
• factorial_fun: ts
• isBeautifulString: js
• composeRanges

類似觀念集中整理

Binary search variants

• SortedSearch - less than - python
• 33. Search in Rotated Sorted Array - python

基礎知識/DSA

algorithms

• sorting
• searching

data structures

tree

tree pre/in/post-order traversal 的定義： https://www.geeksforgeeks.org/tree-traversals-inorder-preorder-and-postorder/

   1
 2   3
4 5

• 所謂的 pre/in/post-order traversal 其實是深度優先（Depth First Traversals）搜尋：
  • (a) Inorder (Left, Root, Right) : [4 2 5 1 3]
  • (b) Preorder (Root, Left, Right) : [1 2 4 5 3]
  • (c) Postorder (Left, Right, Root) : [4 5 2 3 1]
• 而廣度優先（Breadth First or Level Order Traversal）搜尋則會得到： 1 2 3 4 5

Bitwise operation

XOR 特性

https://zh.wikipedia.org/zh-tw/%E9%80%BB%E8%BE%91%E5%BC%82%E6%88%96

基本規則：
p:   0 1 0 1
q:   0 0 1 1
p^q: 0 1 1 0

交換律： p^q = q^p
結合律： (p^q)^r = p^(q^r)
      = q^(r^p)
恆等律： p^0 = p
歸零律： p^p = 0
自反： p^q^q = p^0 = p

Brian Kernighan’s Algorithm (count set bits in an integer)

• 用來計算一個整數的二進位表示法裡有多少的 1
• 很神奇地，做一個 while loop，n > 0，並且將 n 與 (n-1) 做幾次 bitwise &，就能知道有幾個 1

cnt = 0
while (n > 0):
  n = n & (n-1)
  cnt++

Miscellaneous

發現題目直覺暴力解需要 O(n²)，則使用 map 的資料結構歷遍一次(O(n))建立查詢效率 O(1) 的 lookup table，接著再歷遍一次做比較

• 1. Two Sum

參考資料

練習順序

• 👉 https://leetcode.com/problemset/all/?topicSlugs=array
• 🚫 https://books.halfrost.com/leetcode/ChapterTwo/Array/

Dev environment setup

Enable Standard with babel-eslint/parser

references:

1. https://babeljs.io/docs/en/usage
2. https://www.npmjs.com/package/@babel/eslint-parser
3. https://standardjs.com/#how-do-i-use-experimental-javascript-es-next-features

目標是要讓 Standard 看得懂最新的語法，否則有一些 parsing error (e.g. when use class private field, we will get Parsing error: Unexpected character '#') 導致無法做 auto-fix-on-save。

安裝 babel 相關套件

$ npm install --save-dev @babel/core @babel/cli @babel/preset-env

再於 project root path 放置 babel.config.json。以下參考自 babel - Usage Guide 的初始設置範例：

⚠️ 內容可能無所謂，只是為了讓 Standard 運作時不要出現找不到 Babel config 的錯誤

{
  "presets": [
    [
      "@babel/env",
      {
        "targets": {
          "edge": "17",
          "firefox": "60",
          "chrome": "67",
          "safari": "11.1"
        },
        "useBuiltIns": "usage",
        "corejs": "3.6.5"
      }
    ]
  ]
}

安裝 babel-eslint-parser 相關套件

$ npm install eslint @babel/core @babel/eslint-parser --save-dev

再於 project root path 放置 .eslintrc.js，在此指定要使用何種 parser 來做 linting：

module.exports = {
  parser: "@babel/eslint-parser",
};

最後再於 package.js 中設定 standard 使用 @babel/eslint-parser：

{
  ...
  "standard": {
    "parser": "@babel/eslint-parser"
  },
  ...
}

Miscellaneous

指令備忘錄

Go

• test/benchmark (https://my.oschina.net/solate/blog/3034188)
  • go test -bench=. -run=none -benchmem
    • -bench=. 指的是當前路徑
    • -run=none run 原本是用來匹配想要執行的單元測試。不去設定會全跑，若想要全部都不跑就指定一個一定不存在的 pattern (none)
    • -benchmem 打開記憶體配置量量測

folder management

• python createFolder.py -c -t "convertIPv4" create a codesignal problem
• python createFolder.py -l -t "283. Move Zeroes" create a leetcode problem
• npm run ts codesignal/happyNumber/happyNumber.ts

有趣的議題

• bitwise-ops: add overflow detect
• Levenshtein Distance
  • good explanation

Custom badge

• https://shields.io/

Partner

• 🤘 https://github.com/hongtw/coding-life