273. Integer to English Words

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本文介绍了一种将非负整数转换为其英文单词表示的方法，适用于小于2^31-1的输入。通过示例展示了从三位数到十位数的转换过程，并提供了详细的算法实现，包括处理小于1000的数字和使用1000作为分隔符的技巧。

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Description

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”

Problem URL

Solution

给一个int，转化为string的文字的形式

Using a helper to process num < 1000, and use 1000 as a divide.

Code

class Solution {
    private final String[] LESS_20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    private final String[] TENS = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    private final String[] THOUSANDS = {"", "Thousand", "Million", "Billion"};
    public String numberToWords(int num) {
        if (num == 0){
            return "Zero";
        }
        int i = 0;
        String word = "";
        while (num > 0){
            if (num % 1000 != 0){      
                word = helper(num % 1000) + THOUSANDS[i] + " " + word;
            }
            num /= 1000;
            i++;
        }
        
        return word.trim();
        
    }
    
    private String helper(int num){
        if (num == 0){
            return "";
        }
        else if (num < 20){
            return LESS_20[num] + " ";
        }
        else if (num < 100){
            return TENS[num / 10] + " " + helper(num % 10);
        }
        else{
            return LESS_20[num / 100] + " Hundred " + helper(num % 100);
        }
    }
}