[Swift]LeetCode273. 整数转换英文表示 | Integer to English Words

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/10241068.html 
➤如果链接不是山青咏芝的博客园地址，则可能是爬取作者的文章。
➤原文已修改更新！强烈建议点击原文地址阅读！支持作者！支持原创！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

Example 1:

Input: 123
Output: "One Hundred Twenty Three"

Example 2:

Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Example 4:

Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

---

将非负整数转换为其对应的英文表示。可以保证给定输入小于 231 - 1 。

示例 1:

输入: 123
输出: "One Hundred Twenty Three"

示例 2:

输入: 12345
输出: "Twelve Thousand Three Hundred Forty Five"

示例 3:

输入: 1234567
输出: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

示例 4:

输入: 1234567891
输出: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

---

28ms

class Solution {
    func numberToWords(_ num: Int) -> String {
        var lessThan20 = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"];
        var tens = ["", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"];
        var thousands = ["", "Thousand", "Million", "Billion"]
    
        var result = ""
        var i = 0
       var num = num
        
        if num == 0 {
            return "Zero"
        }
        
    func helper(_ num: Int) -> String {
        if num == 0 {
            return ""
        } else if num < 20 {
            return lessThan20[num] + " "
        } else if num < 100 {
            return tens[num / 10] + " " + helper(num % 10)
        } else {
            return lessThan20[num / 100] + " Hundred " + helper(num % 100)
        }
    }
        
    while num > 0 {
        
        if num % 1000 != 0 {
            result = helper(num % 1000) + thousands[i] + " " + result
        }
        num = num / 1000
        
        i += 1
    }
    result = result.trimmingCharacters(in: CharacterSet.whitespaces)
    return result
    }
}

---

28ms

class Solution {
    func numberToWords(_ num: Int) -> String {
        
        if num == 0 {
            return "Zero"
        }
        var num = num
        var res = ""
        let oneBillion = 1000000000
        if num >= oneBillion {
            res += suffixs(num/oneBillion) + " Billion"
            num %= oneBillion
        }
        
        let oneMillion = 1000000
        if num >= oneMillion {
            res += suffixs(num/oneMillion) + " Million"
            num %= oneMillion
        }
        
        let oneThousand = 1000
        if num >= oneThousand {
            res += suffixs(num/oneThousand) + " Thousand"
            num %= oneThousand
        }
        
        if num > 0 {
            res += suffixs(num)
        }
        
        return res.trimmingCharacters(in: .whitespaces)
    }
    
    func suffixs(_ n : Int) -> String {
        let oneNum =  ["One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"]
        let tenNum = ["Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
        let tyNum = ["Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
        var n = n
        var res = ""
        if n > 99 {
            res += " " + oneNum[n/100 - 1] + " Hundred"
        }
        
        n %= 100
        
        if n > 19 {
            res += " " + tyNum[n/10 - 2]
            n %= 10
        }else if n > 9 {
            res += " " + tenNum[n - 10]
            n = 0
        }
        if n > 0 {
            res += " " + oneNum[n - 1]
        }
        
        return res
    }
}

---

36ms

class Solution {
     let zero2TwentyWords = ["Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen","Twenty"]
    
     let  tensWords = ["","Ten","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety","Hundred"]
    let thousandsWords = ["" , "Thousand" , "Million" , "Billion"]
                          
                          
                          
    func numberToWords(_ num: Int) -> String {
     if num == 0 { return "Zero"}
        var temp = num
        var res = ""
        var i = 0
        while temp > 0 {
            if temp % 1000 != 0 {
                res = helper(num: temp % 1000) + thousandsWords[i] + " " + res
            }
            temp = temp / 1000
            i += 1
        }
        return res.trimmingCharacters(in: .whitespacesAndNewlines)
    }

    func helper(num:Int) -> String {
        if num == 0 {
            return ""
        } else if num < 20 {
            return zero2TwentyWords[num % 20] + " "
        } else if num < 100 {
            return tensWords[num / 10] + " " + helper(num: num % 10)
        } else {
            return zero2TwentyWords[num / 100] + " Hundred " + helper(num: num % 100)
        }
    }
    
}