1.js

function findLadders (beginWord, endWord, wordList) {
	let results = []
	let paths = [[beginWord]]

	while (true) {
		findPossibleMutations()

		if (results.length) {
			return results
		}
		if (!paths.length) {
			return []
		}
	}

	function findPossibleMutations () {
		const newPaths = []
		const toExclude = new Set()
		for (const path of paths) {
			const pathLastWord = path[path.length - 1]
			for (const word of wordList) {
				if (canMutate(pathLastWord, word)) {
					toExclude.add(word)
					if (word === endWord) {
						results.push(path.concat([word]))
					} else {
						newPaths.push(path.concat([word]))
					}
				}
			}
		}
		wordList = excludeItems(wordList, toExclude)
		paths = newPaths
	}

	function canMutate (sourceWord, targetWord) {
		let changes = 0
		for (const i in sourceWord) {
			if (sourceWord[i] === targetWord[i]) {
				continue
			}
			changes++
		}
		return changes === 1
	}

	function excludeItems (array, toExclude) {
		return array.filter(w => !toExclude.has(w))
	}
}