package q17

var alphabets = [][]byte{
	[]byte("abc"),
	[]byte("def"),
	[]byte("ghi"),
	[]byte("jkl"),
	[]byte("mno"),
	[]byte("pqrs"),
	[]byte("tuv"),
	[]byte("wxyz"),
}

func combinations(offsets []int, i int, buffer []byte, strings []string) []string {
	if buffer == nil {
		buffer = make([]byte, len(offsets))
	}

	if i == len(offsets) {
		return append(strings, string(buffer))
	}

	for _, c := range alphabets[offsets[i]] {
		buffer[i] = c
		strings = combinations(offsets, i+1, buffer, strings)
	}
	return strings
}

func letterCombinations(digits string) []string {
	offsets := make([]int, len(digits))
	for i := range len(digits) {
		offsets[i] = int(digits[i] - '2')
	}

	return combinations(offsets, 0, nil, []string{})
}

var _ = letterCombinations