273. Integer to English Words

本文主要是介绍273. Integer to English Words，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

问题链接：https://leetcode.com/problems/integer-to-english-words/?tab=Description

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

For example,

123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Hint:

1. Did you see a pattern in dividing the number into chunk of words? For example, 123 and 123000.
2. Group the number by thousands (3 digits). You can write a helper function that takes a number less than 1000 and convert just that chunk to words.
3. There are many edge cases. What are some good test cases? Does your code work with input such as 0? Or 1000010? (middle chunk is zero and should not be printed out)

想了半天还是没什么思路，参照答案默写如下：

public class Solution {private String TENS[] = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};private String LESS_THAN_TWENTY[] = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};private String THOUSANDS[] = {"", "Thousand", "Million", "Billion"};public String numberToWords(int num) {if(num == 0) return "Zero";String result = "";int i = 0;while(num > 0) {if(num%1000 != 0)result = helper(num%1000) + THOUSANDS[i] + " " + result;num = num / 1000;i++;}return result.trim();}private String helper(int value) {if(value == 0)return "";else if(value < 20) {return LESS_THAN_TWENTY[value] + " ";} else if(value < 100) {return TENS[value/10] + " " + helper(value%10);} else {return LESS_THAN_TWENTY[value/100] + " Hundred " + helper(value%100);}}
}

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