leetcode 273. 整数转换英文表示

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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"

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class Solution(object):

    def __init__(self):
        self.lessThan20 = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten",
                       "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
        self.tens = ["", "Ten", "Twenty", "Thirty", "Forty",
                 "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
        self.thousands = ["", "Thousand", "Million", "Billion"]


    def numberToWords(self, num):
        if num == 0:
            return "Zero"
        res = ""
        for i in range(len(self.thousands)):
            if num % 1000 != 0:
                res = self.helper(num % 1000) + self.thousands[i] + " " + res
            num /= 1000
        return res.strip()


    def helper(self, num):
        if num == 0:
            return ""
        elif num < 20:
            return self.lessThan20[num] + " "
        elif num < 100:
            return self.tens[num/10] + " " + self.helper(num % 10)
        else:
            return self.lessThan20[num/100] + " Hundred " + self.helper(num % 100)