如何访问循环内的先前值？

Question

我对 JS 编程有点陌生，如果这是一个明显的问题，我很抱歉。我有一个代码可以计算字符串中重复的字母。代码应该只输出使用两次以上的字母。

例如：

let str = "HELLOWORLD"

输出应为：L = 3, O = 3

我的代码输出：L =3, O = 2, O =2, L = 3

我想去掉第二个O和L

function repeat(){
    let str = "helloworld";
    let letters = "";
    let count = "";
    let output = "";
    let x = "";
    for (i = 0; i <str.length; i++){
    letters = str.charAt(i); 
    count = str.split(letters).length - 1;
    if (count >= 2 && x !== letters) {
    output += letters +"=" + count + " ";
    }
    x = letters;
}
console.log(output);
}

repeat();

由于 x = letters; 代码，我只能删除出现在新字母之前的重复字母。我希望这些字符只出现一次，但我很难处理循环。我知道它看起来很乱并且需要改进，但我会在找到解决方案后继续努力。如有任何建议，我们将不胜感激！

Answer 1

你可以这样做：

var strs = "helloworld";

const output = strs.split('').reduce(function(prev, cur) {
  prev[cur] = (prev[cur] || 0) + 1;
  return prev;
}, {});

const convertToArray = Object.entries(output);
const filterMorethan2 = convertToArray.filter(([key, value]) => value >= 2);

const converBackObj = Object.fromEntries(filterMorethan2);
console.log(converBackObj)

编码愉快!!!

Answer 2

您可以将重复的字母保存在一个数组中，然后检查该字母是否已经存在。

function repeat(){
    let str = "helloworld";
    let letters = "";
    let count = "";
    let output = "";
    let x = "";
    let multipleChars = [];
    for (i = 0; i <str.length; i++){
    letters = str.charAt(i);
    count = str.split(letters).length - 1;
    if (count >= 2 && x !== letters && !multipleChars.includes(letters)) {
    output += letters +"=" + count + " ";
    multipleChars.push(letters);
    }
    x = letters;
}
console.log(output);
}

repeat();

Answer 3

一种常用方法是使用 an object to maintain a count of the letters - the letters are the property keys, and the value is the number that gets increased whenever that letter is found. We can then loop over that object 并仅记录那些值大于 2 的属性。

function repeat(str) {

  // Create the object
  const obj = {};

  // Loop over the string
  for (let i = 0; i < str.length; i++) {

    const letter = str[i];

    // If the letter (key) doesn't already exist
    // on the object create it, and set the value to zero
    // then immediately increase it by one
    if (obj[letter] === undefined) {
      obj[letter] = 0;
    }

    obj[letter] += 1;

  }

  // So we have an object that contains _all_ the
  // letters, so now we loop over it to print out
  // only those with values greater than two
  // We can use a template string:
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals
  for (let letter in obj) {
    if (obj[letter] > 2) {
      console.log(`${letter} = ${obj[letter]}`);
    }  
  }

}

repeat('helloworld');

Answer 4

使用你的 js 工具箱：

let str = 'HelloWorld';

let a = Object.entries([...str].reduce((r,c)=>{
  r[c]=(r[c] || 0) +1;
  return r;
},{})).filter(e=>e[1]>2).sort(([,a],[,b]) => b-a).reduce((s,i,idx)=>(`${s}${idx>0 ? ", " : ""}${i.join('=')}`),'');

console.log(a);

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