package q433

import "slices"

func canMutate(a, b string) bool {
	diff := false
	for i := range len(a) {
		if a[i] != b[i] {
			if diff {
				return false
			}
			diff = true
		}
	}
	return diff // exactly one mutation
}

func minMutation(startGene string, endGene string, bank []string) int {
	reachables := make([][]int, len(bank))
	initial := []int{}
	target := -1
	for i := range len(bank) - 1 {
		for j := i + 1; j < len(bank); j++ {
			if canMutate(bank[i], bank[j]) {
				reachables[i] = append(reachables[i], j)
				reachables[j] = append(reachables[j], i)
			}
		}
	}
	for i := range bank {
		if bank[i] == endGene {
			target = i
		}
		if canMutate(startGene, bank[i]) {
			if i == target {
				return 1
			}
			initial = append(initial, i)
		}
	}
	if target == -1 {
		return -1
	}

	type qElem struct {
		path []int
	}
	queue := make([]qElem, 0, len(initial)*2)
	for _, i := range initial {
		queue = append(queue, qElem{path: []int{i}})
	}

	for ; len(queue) > 0; queue = queue[1:] {
		cur := queue[0].path
		last := cur[len(cur)-1]
		next := reachables[last]
		for _, n := range next {
			if n == target {
				return len(cur) + 1
			}
			if slices.Contains(cur, n) {
				continue
			}
			queue = append(queue, qElem{path: append(cur, n)})
		}
	}

	return -1
}

var _ = minMutation