leetcode-go/leetcode/hard/273.integer-to-english-words.go

func numberToWords(num int) string {
	if num == 0 {
		return "Zero"
	}
	return ntowRecurse(num)
}

func ntowRecurse(num int) (res string) {
	if num/1000000000 != 0 {
		res += ntowRecurse(num/1000000000) + getWord(0) + getWord(1000000000) + getWord(0) + ntowRecurse(num%1000000000)
	} else if num/1000000 != 0 {
		res += ntowRecurse(num/1000000) + getWord(0) + getWord(1000000) + getWord(0) + ntowRecurse(num%1000000)
	} else if num/1000 != 0 {
		res += ntowRecurse(num/1000) + getWord(0) + getWord(1000) + getWord(0) + ntowRecurse(num%1000)
	} else if num/100 != 0 {
		res += ntowRecurse(num/100) + getWord(0) + getWord(100) + getWord(0) + ntowRecurse(num%100)
	} else if 20 <= num {
		res += getWord(num-num%10) + getWord(0) + ntowRecurse(num%10)
	} else if num != 0 {
		res = getWord(num)
	}
	return strings.Trim(res, " ")
}

func getWord(num int) string {
	switch num {
	case 1:
		return "One"
	case 2:
		return "Two"
	case 3:
		return "Three"
	case 4:
		return "Four"
	case 5:
		return "Five"
	case 6:
		return "Six"
	case 7:
		return "Seven"
	case 8:
		return "Eight"
	case 9:
		return "Nine"
	case 10:
		return "Ten"
	case 11:
		return "Eleven"
	case 12:
		return "Twelve"
	case 13:
		return "Thirteen"
	case 14:
		return "Fourteen"
	case 15:
		return "Fifteen"
	case 16:
		return "Sixteen"
	case 17:
		return "Seventeen"
	case 18:
		return "Eighteen"
	case 19:
		return "Nineteen"
	case 20:
		return "Twenty"
	case 30:
		return "Thirty"
	case 40:
		return "Forty"
	case 50:
		return "Fifty"
	case 60:
		return "Sixty"
	case 70:
		return "Seventy"
	case 80:
		return "Eighty"
	case 90:
		return "Ninety"
	case 100:
		return "Hundred"
	case 1000:
		return "Thousand"
	case 1000000:
		return "Million"
	case 1000000000:
		return "Billion"
	default:
		return " "
	}
}