alphabet-board-path.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 }
	
	const ret = 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('')
	
	return ret
}