LeetCode：Integer to English Words - 按英語讀法輸出數字對應單詞

一、題目名稱

Integer to English Words（按英語讀法輸出數字對應單詞）

二、題目地址

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

三、題目內容

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

中文：給出一個非負整數，輸出該數字在英語對應的單詞，數字小於2^31-1

例如：下面是三個轉換的例子

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

四、解題方法

其實一開始我把題目想複雜了。這道題不用考慮英語中隔位要寫「And」的狀況。如101，在英語中的念法爲「One Hundred And One」，在這道題中，只須要輸出「One Hundred One」就能夠了。所以，要AC本題只須要將對應位置的數字和數位寫對。Java代碼以下：

/**
 * @功能說明：LeetCode 273 - Integer to English Words
 * @開發人員：Tsybius2014
 * @開發時間：2015年10月12日
 */
public class Solution {
    
    /**
     * 按英語讀法輸出阿拉伯數字對應單詞
     * @param num 數字，範圍：[0,2^31-1]
     * @return
     */
    public String numberToWords(int num) {
        
        if (num < 0) {
            return "";
        }

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

        //左起段落
        int segment1 = num / 1000000000;           //段落1：十億位-千億位
        int segment2 = num % 1000000000 / 1000000; //段落2：百萬位-億位
        int segment3 = num % 1000000 / 1000;       //段落3：千位-十萬位
        int segment4 = num % 1000;                 //段落4：個位-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();
    }
    
    /**
     * 按英語讀法輸出阿拉伯數字對應單詞
     * @param num 數字，範圍：(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;
    }

    /**
     * 按英語讀法輸出阿拉伯數字對應單詞
     * @param num 數字，範圍：(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