index.ts

// TODO: Refactor Me

export const frequencySort = (str: string) => {
  const charactorFrequency = countCharactorFrequency(str)
  const sortedFrequency = getSortedFrequency(charactorFrequency)

  let res = []
  for (let i = 0; i < sortedFrequency.length; i++) {
    res.push(
      ...Array(charactorFrequency[sortedFrequency[i]]).fill(
        String.fromCharCode(sortedFrequency[i]),
      ),
    )
  }

  return res.join('')
}

const countCharactorFrequency = (str: string) => {
  const charactorFrequency = Array(128).fill(0)
  for (let i = 0; i < str.length; i++) {
    charactorFrequency[str.charCodeAt(i)]++
  }

  return charactorFrequency
}

const getSortedFrequency = (charactorFrequency: number[]) => {
  const sortedFrequency = [0]
  for (let i = 1; i < charactorFrequency.length; i++) {
    for (let j = 0; j < sortedFrequency.length; j++) {
      if (charactorFrequency[i] >= charactorFrequency[sortedFrequency[j]]) {
        sortedFrequency.splice(j, 0, i)
        break
      }
    }
  }

  return sortedFrequency
}