Isogram

等级:7kyu

原始题目isogram的解释

An isogram is a word that has no repeating letters, consecutive or non-consecutive. Implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.

中翻:字串中一个字母只出现一次(不分大小写)，若符合条件则回传true(空字串也视为Isogram)。

isIsogram "Dermatoglyphics" == true
isIsogram "aba" == false
isIsogram "moOse" == false -- ignore letter case

自解:

export function isIsogram(str: string){
  let lowerCaseStr = str.toLowerCase(); 
  let arr = lowerCaseStr.split("");
  let setArrNumber = new Set(arr).size
  if(setArrNumber !== arr.length){
    return false
  }
  else{
    return true
  }
}

好像有点冗长，後来查到一位的写法比我精简许多(查看下方)，但想法是相同的。
概念是:

1. 先将字串全部转成lowerCase
2. 将字串的每个字母拆解
3. 去比对字母是否有重复，透过new Set()可以让所有的值都是唯一的，若有值重复则会被忽略，
   所以去比较Set完後的元素数量(透过set.prototype.size)是否和原本拆解的字母阵列数量相同，
   若不同则代表有重复字母，回传false，反之则回传true

他解1:

author: fullstackdevguy

export function isIsogram(str: string){
  //resolve str to lowercase first
  str = str.toLowerCase();
  //transform string to a Set to remove duplicates and 
  //compare the size of the set to the length of the str
  return new Set(str.split('')).size === str.length;
}

他解2:

author: stellartux

export function isIsogram (str: string): boolean {
  return (new Set(str.toLowerCase())).size === str.length
}

超级精简的code~~ 十分佩服

此次题目使用到的方法和参考网址:

array.split()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split

String.prototype.toLowerCase()
https://developer.mozilla.org/zh-TW/docs/Web/JavaScript/Reference/Global_Objects/String/toLowerCase

Set.prototype.size
https://www.fooish.com/javascript/ES6/Set-and-WeakSet.html
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/size