2022-01-09：整数转换英文表示。将非负整数 num 转换为其对应的英文表示。

示例 1：

输入：num = 123，

输出：”One Hundred Twenty Three”。

力扣273。

答案2022-01-09：

时间紧。具体见代码。

代码用golang编写。代码如下：

 package main

import (
    "fmt"
    "math"
    "strings"
)

func main() {
    num := 123
    ret := numberToWords(num)
    fmt.Println(ret)
}

func num1To19(num int) string {
    if num < 1 || num > 19 {
        return ""
    }
    names := []string{"One ", "Two ", "Three ", "Four ", "Five ", "Six ", "Seven ", "Eight ", "Nine ", "Ten ",
        "Eleven ", "Twelve ", "Thirteen ", "Fourteen ", "Fifteen ", "Sixteen ", "Seventeen", "Eighteen ",
        "Nineteen "}
    return names[num-1]
}

func num1To99(num int) string {
    if num < 1 || num > 99 {
        return ""
    }
    if num < 20 {
        return num1To19(num)
    }
    high := num / 10
    tyNames := []string{"Twenty ", "Thirty ", "Forty ", "Fifty ", "Sixty ", "Seventy ", "Eighty ", "Ninety "}
    return tyNames[high-2] + num1To19(num%10)
}

func num1To999(num int) string {
    if num < 1 || num > 999 {
        return ""
    }
    if num < 100 {
        return num1To99(num)
    }
    high := num / 100
    return num1To19(high) + "Hundred " + num1To99(num%100)
}

func numberToWords(num int) string {
    if num == 0 {
        return "Zero"
    }
    res := ""
    if num < 0 {
        res = "Negative "
    }
    if num == math.MinInt64 {
        res += "Two Billion "
        num %= -2000000000
    }
    num = Abs(num)
    high := 1000000000
    highIndex := 0
    names := []string{"Billion ", "Million ", "Thousand ", ""}
    for num != 0 {
        cur := num / high
        num %= high
        if cur != 0 {
            res += num1To999(cur)
            res += names[highIndex]
        }
        high /= 1000
        highIndex++
    }
    return strings.Trim(res, " ")
}

func Abs(a int) int {
    if a < 0 {
        return -a
    } else {
        return a
    }
}  

执行结果如下：

***

[左神java代码](