LeetCode：Integer to English Words

某厂面试归来，发现自己落伍了！>>>

1、题目名称

Integer to English Words（按英语读法输出数字对应单词）

2、题目地址

https://leetcode.com/problems/integer-to-english-words/

3、题目内容

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

中文：给出一个非负整数，输出该数字在英语对应的单词，数字小于2^31-1

例如：下面是三个转换的例子

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

4、解题方法

其实一开始我把题目想复杂了。这道题不用考虑英语中隔位要写“And”的情况。如101，在英语中的念法为“One Hundred And One”，在这道题中，只需要输出“One Hundred One”就可以了。因此，要AC本题只需要将对应位置的数字和数位写对。Java代码如下：

/**
 * @功能说明：LeetCode 273 - Integer to English Words
 * @开发人员：Tsybius2014
 * @开发时间：2015年10月12日
 */
public class Solution {
    
    /**
     * 按英语读法输出阿拉伯数字对应单词
     * @param num 数字，范围：[0,2^31-1]
     * @return
     */
    public String numberToWords(int num) {
        
        if (num < 0) {
            return "";
        }

        //数字为0直接返回
        if (num == 0) {
            return "Zero";
        }

        //左起段落
        int segment1 = num / 1000000000;           //段落1：十亿位-千亿位
        int segment2 = num % 1000000000 / 1000000; //段落2：百万位-亿位
        int segment3 = num % 1000000 / 1000;       //段落3：千位-十万位
        int segment4 = num % 1000;                 //段落4：个位-百位

        String result = "";
        
        if (segment1 > 0) {
            result += numToWordsLessThan1000(segment1) + " " + "Billion";
        }
        if (segment2 > 0) {
            result += numToWordsLessThan1000(segment2) + " " + "Million";
        }
        if (segment3 > 0) {
            result += numToWordsLessThan1000(segment3) + " " + "Thousand";
        }
        if (segment4 > 0) {
            result += numToWordsLessThan1000(segment4);
        }

        return result.trim();
    }
    
    /**
     * 按英语读法输出阿拉伯数字对应单词
     * @param num 数字，范围：(0,1000)
     * @return
     */
    private String numToWordsLessThan1000(int num) {
        
        if (num == 0 || num >= 1000) {
            return "";
        }
        
        String result = "";
        if (num >= 100) {
            result += numToWordsBase(num / 100) + " " + "Hundred";
        }
        num = num % 100;
        if (num > 20) {
            result += numToWordsBase(num / 10 * 10);
            if (num % 10 != 0) { 
                result += numToWordsBase(num % 10);
            }
        } else if (num > 0) {
            result += numToWordsBase(num);
        }
        
        return result;
    }

    /**
     * 按英语读法输出阿拉伯数字对应单词
     * @param num 数字，范围：(0,20)∪{30,40,50,60,70,80,90}
     * @return
     */
    private String numToWordsBase(int num) {
        String result = " ";
        switch (num) {
        case 1: result += "One"; break;
        case 2: result += "Two"; break;
        case 3: result += "Three"; break;
        case 4: result += "Four"; break;
        case 5: result += "Five"; break;
        case 6: result += "Six"; break;
        case 7: result += "Seven"; break;
        case 8: result += "Eight"; break;
        case 9: result += "Nine"; break;
        case 10: result += "Ten"; break;
        case 11: result += "Eleven"; break;
        case 12: result += "Twelve"; break;
        case 13: result += "Thirteen"; break;
        case 14: result += "Fourteen"; break;
        case 15: result += "Fifteen"; break;
        case 16: result += "Sixteen"; break;
        case 17: result += "Seventeen"; break;
        case 18: result += "Eighteen"; break;
        case 19: result += "Nineteen"; break;
        case 20: result += "Twenty"; break;
        case 30: result += "Thirty"; break;
        case 40: result += "Forty"; break;
        case 50: result += "Fifty"; break;
        case 60: result += "Sixty"; break;
        case 70: result += "Seventy"; break;
        case 80: result += "Eighty"; break;
        case 90: result += "Ninety"; break;
        }
        return result;
    }
}

END

来源：oschina

链接：https://my.oschina.net/u/1425762/blog/516047