crack-caesar-code.js

// Crack caesard encoded sentences.
// By find which letter is E.
// E is letter the most used in french.
function crack(caesarCode) {
  const matrix = {};
  const caesarCodeArray = caesarCode.toUpperCase().split('')
  caesarCodeArray.filter(e => e !== " ").forEach(e => {
    if(matrix[e]) {
      matrix[e] += 1
    } else {
      matrix[e] = 1
    }
  })

  console.log('matrix', matrix)

  const maxValue = Object.values(matrix).sort((a, b) => b - a)[0]
  console.log('maxValue', maxValue)
  const E = Object.keys(matrix).find(e => matrix[e] === maxValue)
  // console.log('E === ', E)

  const alpha = [...'ABCDEFGHIJKLMNOPQRSTUVWXYZ']
  const decalage = alpha.indexOf(E)  - alpha.indexOf('E')
  // console.log('decalage', decalage)
  let alphaShifted = alpha.slice(decalage, alpha.length)
  alphaShifted.push(...alpha.slice(0, decalage))
  // console.log('alphaShifted', alphaShifted)

  const answer = caesarCodeArray.reduce((acc, curr) => {
    if (!alpha.includes(curr)) {
      return acc + curr
    }
    return acc + alpha[alphaShifted.indexOf(curr)]
  }, '')
  return answer
}

console.log(
  crack("Cv tfuv Tvjri vjk le tyzwwivdvek srjv jli le uvtrcrxv uv c'rcgyrsvk (uvgcrtvdvek uvj cvkkivj gclj cfze urej c'rcgyrsvk), zc j'rxzk u'lev jlsjkzklkzfe dfefrcgyrsvkzhlv, t'vjk-r-uziv hl'lev dvdv cvkkiv e'vjk ivdgcrtvv hlv gri lev jvlcv rlkiv (kflaflij zuvekzhlv gfli le dvdv dvjjrxv). Cv uvtrcrxv cv gclj jflmvek lkzczjv vjk uv kifzj cvkkivj.")
)