Integer to English words leetcode java

问题描述：

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"

方法一：自己写的，没有层次感，看起来不够清晰

 static String[][] enStr = {
            {"","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen",
                "Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"}, //1-19
            {"","","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"} // 20-90
    };
    public String numberToWords(int num) {
       if(num < 0) //非负整数
            return null;
        String english = "";
        int remain = 0;
        if(num / 20 == 0) {//1-19
            if(num == 0) //num == 0单独处理
                return "Zero";
            return enStr[0][num];
        } else if(num / 100 == 0){ //20-99
            if(num % 10 == 0) //若是20,30,40,50,...,90
                return enStr[1][num / 10];
            else
                return enStr[1][num / 10] + " " + enStr[0][num % 10];
        } else if(num / 1000 == 0){//100-999
            int h = num / 100;
            remain = num % 100;
            if(remain >= 20 && remain % 10 ==0){
                english = enStr[0][h] + " Hundred " + enStr[1][remain / 10];
            } else if(remain >= 20 && remain % 10 > 0){
                english = enStr[0][h] + " Hundred " + enStr[1][remain / 10] + " " + enStr[0][remain % 10];
            } else if(remain == 0){
                english = enStr[0][h] + " Hundred";
            } else {
                english = enStr[0][h] + " Hundred " + enStr[0][remain];
            }
            return english;
        } else if(num / 1000000 == 0){ //1000-999999
            int th = num / 1000;
            remain = num % 1000;
            if(remain == 0){
                return numberToWords(th) + " Thousand";
            }
            return  numberToWords(th) + " Thousand " + numberToWords(remain);
        } else if(num / 1000000000 == 0) {//1000000-999999999
            int mi = num / 1000000;
            remain = num % 1000000;
            if(remain == 0){
                return numberToWords(mi) + " Million";
            }
            return  numberToWords(mi) + " Million " + numberToWords(remain);
        } else { //1000000000-9999999999
            int bi = num / 1000000000;
            remain = num % 1000000000;
            if(remain == 0){
                return numberToWords( bi) + " Billion";
            }
            return numberToWords(bi) + " Billion " + numberToWords(remain);
        }
    }

方法二：代码整齐，参考别人的

 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(); //去掉字符串首尾的空格
    }

   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;
    }

    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;
    }