封面画师: あずーる

twitter：@azure_0608_sub

题目链接：https://leetcode-cn.com/problems/integer-to-english-words/

主要是准确度的问题，英语中三位换千、百万、十亿，在数学上不难，就是烦。

答案仅适用于int32，因为题目写明：0 <= num <= 231 - 1

var Enumber = [...]string{"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight","Nine","Ten","Eleven","Twelve","Thirteen", "Fourteen", "Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"}
var Mnumber = [10]string{"","","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"}
var BMT = [4]string{"Billion", "Million", "Thousand", ""}

func numberToWords(num int) string {
    if num == 0 {
        return Enumber[0] //直接返回Zero
    }
    sb := strings.Builder{}
    for i, j := 1000000000, 0; i > 0; i, j = i/1000, j+1 {
        if num < i {
            continue
        }
        sb.WriteString(numToStr(num/i) + BMT[j] + " ")
        num %= i
    }
    return strings.TrimSpace(sb.String())
}

func numToStr(x int) (ans string) {
    if x >= 100 {
        ans += Enumber[x/100] + " Hundred "
        x %= 100
    }
    if x >= 20 {
        ans += Mnumber[x/10] + " "
        x %= 10
    }
    if x != 0 {
        ans += Enumber[x] + " "
    }
    return
}

在十位数控制的时候Mnumber[0]和 Mnumber[1]留""方便后面操作，不加入Hundred主要是为了后面判断位数再加。