JAVASCRIPT 计算字符串中小写字母的出现次数

Question

我有一个javascript问题让我很困惑

Write a function stringCase that takes a string with mixed uppercase and lowercase characters and return the string in either all uppercase or all lowercase depending on which letter case the string has more of. If the string has equal upper and lower case characters, convert the string to all lowercase. Do not include any loops, length property, or native methods (exception: toLowerCase() & toUpperCase() allowed).

我可以立即想到一些解决这个问题的方法，比如使用循环来检查每个字符，或者使用替换方法和正则表达式并获取结果的长度。但是，提示禁止我使用循环，长度属性，和native方法

如有任何帮助，我们将不胜感激。提前致谢！

Answer 1

这里的技巧是使用递归来做循环。您可以手动跟踪指针和计数。

const stringCase = (s) => {
  let i = 0;
  let count = 0;

  const process = () => {
    const curr = s[i++];
    if (!curr) {
      return count <= 0 ? s.toLowerCase() : s.toUpperCase();
    }

    if (curr.toLowerCase() === curr) {
      count--
    } else {
      count++
    }

    return process();
  }
  
  return process();
};

console.log(stringCase('Aa') === 'aa');
console.log(stringCase('AaA') === 'AAA');
console.log(stringCase('aa') === 'aa');
console.log(stringCase('AA') === 'AA');

Answer 2

所以我的回答与 JBallin 的类似，只是我使用频率计数器来跟踪大小写计数。这减少了辅助功能的移动部件数量。

function convertString(str) {
    // object to keep track frequency of upper/lower case letters
    const frequencyCounter = {
        upper: 0,
        lower: 0
    }

    let currentIndex = 0

    // helper function to increment frequencies of letters
    function checkCase() {
        const currentChar = str[currentIndex]

        // if current index is outside length of string and returns undefined
        // break recursive loop by returning
        if (!currentChar) return

        if (currentChar.toUpperCase() === currentChar) {
            frequencyCounter.upper +=1;
        } else {
            frequencyCounter.lower +=1;
        }

        // increment current index and recursively call helper function
        currentIndex++
        return checkCase()
    }

    // start helper function
    checkCase()

    // check for which case to convert the string to and return that string
    if (frequencyCounter.upper > frequencyCounter.lower) {
        return str.toUpperCase();
    } else {
        return str.toLowerCase();
    }
}

JAVASCRIPT 计算字符串中小写字母的出现次数

JAVASCRIPT Count occurrences of lower case letters in a string

javascript

string

char