package wordladder

import "iter"

type wordSet map[string][]string

func (w wordSet) add(word string) {
	buffer := []byte(word)
	for i := range word {
		buffer[i] = '*'
		w[string(buffer)] = append(w[string(buffer)], word)
		buffer[i] = word[i]
	}
}

func (w wordSet) neighborsOf(word string) iter.Seq[string] {
	return func(yield func(string) bool) {
		buffer := []byte(word)
		for i := range word {
			buffer[i] = '*'
			for _, neighbor := range w[string(buffer)] {
				yield(neighbor)
			}
			buffer[i] = word[i]
		}
	}
}

func ladderLength(beginWord string, endWord string, wordList []string) int {
	ws := wordSet{}
	for _, word := range wordList {
		ws.add(word)
	}

	idx, iteration, visited := 0, []string{beginWord}, map[string]bool{}
	visited[beginWord] = true

	for {
		nextIteration := []string{}
		for _, it := range iteration {
			if it == endWord {
				return idx
			}

			for neighbor := range ws.neighborsOf(it) {
				if visited[neighbor] {
					continue
				}

				visited[neighbor] = true
				nextIteration = append(nextIteration, neighbor)
			}
		}

		iteration = nextIteration
		idx++
	}

	return 0
}