alphabet-board-path.clean.js

const alphabetBoardPath = (target) => {
  const layout = 5
  const hashMap = new Map(Array.from("abcdefghijklmnopqrstuvwxyz").map((c, i) => [ c,  {x: (i / layout) | 0, y: i % layout | 0}]))
  const repeat = (s, n) => (n <= 0 ? '' : s.repeat(n))
  let p0 = { x: 0, y: 0 }
  return Array.from(target).reduce((ret, t) => {
    const p = hashMap.get(t)
    ret.push(p.y < p0.y ? repeat('L', p0.y - p.y) : '', p.x < p0.x ? repeat('U', p0.x - p.x) : '', p.x > p0.x ? repeat('D', p.x - p0.x) : '', p.y > p0.y ? repeat('R', p.y - p0.y) : '', '!')
    p0 = p
    return ret
  }, []).join('')
}