LeetCode解題筆記 40 —— 273. 整數轉換英文表示

題目

將非負整數轉換爲其對應的英文表示。可以保證給定輸入小於 2^31 - 1 。

示例 1:

輸入: 123
輸出: "One Hundred Twenty Three"

示例 2:

輸入: 12345
輸出: "Twelve Thousand Three Hundred Forty Five"

示例 3:

輸入: 1234567
輸出: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

示例 4:

輸入: 1234567891
輸出: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

解法

class Solution {
    public String numberToWords(int num) {
        if(num == 0){
            return "Zero";
        }
        StringBuilder b = new StringBuilder();
        String str = String.valueOf(num);
        if(str.length() > 9){
            b.append(toEnglish(str.substring(0,str.length()-9))).append("Billion ");
            str = str.substring(str.length()-9);
        }
        if(str.length() > 6){
            String s = toEnglish(str.substring(0,str.length()-6));
            if(!s.trim().equals("")){
                  b.append(s).append("Million ");
            }
            str = str.substring(str.length()-6);
        }
        if(str.length() > 3){
            String s = toEnglish(str.substring(0,str.length()-3));
            if(!s.trim().equals("")){
                  b.append(s).append("Thousand ");
            }
            str = str.substring(str.length()-3);
        }
        b.append(toEnglish(str));
        String res =  b.toString().trim();
        while(res.contains("  ")){
            res = res.replace("  "," ");
        }
        return res;
    }
    
    
    private String toEnglish(String str){
        StringBuilder b = new StringBuilder();
        if(str.length()>2){
            char c = str.charAt(str.length()-3);
            if(c!='0'){
                b.append(getNum(c)).append(" Hundred ");
            }
        }
        boolean flag = true;
        if(str.length()>1){
            char c = str.charAt(str.length()-2);
            if(c!='0'){
                if(c=='1'){
                    flag = false;
                    b.append(getNumteen(str.charAt(str.length()-1))).append(" ");
                }else{
                    b.append(getNumty(c)).append(" ");
                }
            }
        }
        if(str.length()>0 && flag){
            char c = str.charAt(str.length()-1); 
            b.append(getNum(c)).append(" ");
        }
        return b.toString();
    }
    
    private String getNum(char c){
        switch(c){
            case '0':
                return "";
            case '1':
                return "One";
            case '2':
                return "Two";
            case '3':
                return "Three";
            case '4':
                return "Four";
            case '5':
                return "Five";
            case '6':
                return "Six";
            case '7':
                return "Seven";
            case '8':
                return "Eight";
            case '9':
                return "Nine";
            default:
                return "";
        }
    }
    private String getNumty(char c){
        switch(c){
            case '2':
                return "Twenty";
            case '3':
                return "Thirty";
            case '4':
                return "Forty";
            case '5':
                return "Fifty";
            case '6':
                return "Sixty";
            case '7':
                return "Seventy";
            case '8':
                return "Eighty";
            case '9':
                return "Ninety";
            default:
                return "";
        }
    }
    
     private String getNumteen(char c){
        switch(c){
            case '0':
                return "Ten";
            case '1':
                return "Eleven";
            case '2':
                return "Twelve";
            case '3':
                return "Thirteen";
            case '4':
                return "Fourteen";
            case '5':
                return "Fifteen";
            case '6':
                return "Sixteen";
            case '7':
                return "Seventeen";
            case '8':
                return "Eighteen";
            case '9':
                return "Nineteen";
            default:
                return "";
        }
    }
}