Discussion on: Daily Challenge #60 - Find the Missing Letter

[Chris Achard]

Here it is in JS, uses charCodeAt and fromCharCode to convert from char to ASCII number, then looks for the number difference of 2 (missing number in between them):

const missing = arr => {
  for(let i in arr) {
    const letter = arr[i]
    const next = arr[Number(i) + 1]
    if(next.charCodeAt(0) - letter.charCodeAt(0) === 2
    ) {
      return String.fromCharCode(arr[i].charCodeAt(0) + 1)
    }
  }
}

[Kamaal Aboothalib]

Almost identical but I try with the functional approach and typescript
checks any number of chars instead of one.

const getDiff = (a:number, b: number):number => b - a
const getGap = (a:number, maxDiff:number = 1):number => a - maxDiff
const fillGaps = (a:number, gap:number):string[] => gap > 0 ? [...(Array(gap).fill(0))].map((_, e) => e + 1 )
    .map(i => i + a )
    .map(i => String.fromCharCode(i)) : []

const missing = (input:string[]): string => {
  return input.reduce((a, b, index, array) => {
    const positionIndex = `${b}`.charCodeAt(0)
    const nextPositionIndex:number = index + 1 < array.length ? array[index+1].charCodeAt(0) : positionIndex
    const gap = getGap(getDiff(positionIndex, nextPositionIndex), 1)
    const gaps = fillGaps(positionIndex, gap)
    return [...a,...gaps]
  }, []).join(', ')
}

codesandbox.io/s/quirky-davinci-sk826