LeetCode Integer To Roman & Roman To Int

罗马数字

 有几条须注意掌握；
  (1)基本数字Ⅰ、X 、C 中的任何一个，自身连用构成数目，或者放在大数的右边连用构成数目，都不能超过三个；放在大数的左边只能用一个。
  (2)不能把基本数字 V 、L 、D 中的任何一个作为小数放在大数的左边采用相减的方法构成数目；放在大数的右边采用相加的方式构成数目，只能使用一个。
  (3)V 和 X 左边的小数字只能用Ⅰ。
  (4)L 和 C 左边的小数字只能用×。
  (5)D 和 M 左 边的小数字只能用 C 。

【对照举例】
·个位数举例
        I, 1     II, 2      III, 3     IV, 4     V, 5      VI, 6     VII, 7    VIII,8      IX, 9 

·十位数举例
  X, 10   XI, 11    XII, 12     XIII, 13    XIV, 14  XV, 15      XVI, 16       XVII, 17      XVIII, 18      XIX, 19      XX, 20  XXI, 21     XXII, 22     XXIX, 29       XXX, 30    XXXIV, 34        XXXV, 35       XXXIX, 39     XL, 40    L, 50       LI, 51    LV, 55     LX, 60     LXV, 65   LXXX, 80      XC, 90      XCIII, 93    XCV, 95     XCVIII, 98      XCIX, 99   

·百位数举例
   C, 100     CC, 200   CCC, 300    CD, 400    D, 500  DC,600 DCC, 700      DCCC, 800     CM, 900   CMXCIX,999      
                                                                                                                                                                    
·千位数举例                              
    M, 1000     MC, 1100     MCD, 1400        MD, 1500       MDC, 1600   MDCLXVI, 1666      MDCCCLXXXVIII, 1888     MDCCCXCIX, 1899 MCM, 1900    MCMLXXVI, 1976      MCMLXXXIV, 1984     MCMXC, 1990       MM, 2000       MMMCMXCIX, 3999

另外参考 http://blog.csdn.net/menxu_work/article/details/9147209

方法一:

    public String intToRoman(int num) {
                StringBuilder stringBuilder=new StringBuilder();
        int i=num;
        if(num>=1000 && num<4000)
        {
            int j=i/1000;
            while(j-->0)
            {
                stringBuilder.append('M');
            }
            stringBuilder.append(intToRoman(i%1000));
        }
        else if(num>=900 && num<1000)
        {
            stringBuilder.append("CM"+intToRoman(i%900));
        }
        else if(num>=500 && num<900)
        {
            stringBuilder.append("D"+intToRoman(i%500));
        }
        else if(num>=400 && num<500)
        {
            stringBuilder.append("CD"+intToRoman(i%400));
        }
        else if(num>=100 && num<400)
        {
            int j=i/100;
            while(j-->0)
            {
                stringBuilder.append('C');
            }
            stringBuilder.append(intToRoman(i%100));
        }
        else if(num>=90 && num<100)
        {
            stringBuilder.append("XC"+intToRoman(i%90));
        }
        else if(num>=50 && num<90)
        {
            stringBuilder.append("L"+intToRoman(i%50));
        }
        else if(num>=40 && num<50)
        {
            stringBuilder.append("XL"+intToRoman(i%40));
        }
        else if(num>=10 && num<40)
        {
            int j=i/10;
            while(j-->0)
            {
                stringBuilder.append('X');
            }
            stringBuilder.append(intToRoman(i%10));
        }
        else if(num>=9 && num<10)
        {
            stringBuilder.append("IX");
        }
        else if(num>=5 && num<9)
        {
            stringBuilder.append("V"+intToRoman(i%5));
        }
        else if(num>=4 && num<5)
        {
            stringBuilder.append("IV");
        }
        else if(num>=1 && num<4)
        {
            while(i-->0)
            {
                stringBuilder.append('I');
            }
        }
        return stringBuilder.toString();
    }

方法二:

    public String intToRoman(int num) {
        int [] vals={1000,900,500,400,100,90,50,40,10,9,5,4,1};
        String[] romans={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
        StringBuilder stringBuilder=new StringBuilder();
        for(int i=0;i<vals.length;i++)
        {
            while(num>=vals[i])
            {
                num-=vals[i];
                stringBuilder.append(romans[i]);
            }
        }
        return stringBuilder.toString();
    }

Roman To Int

        int [] vals={1000,900,500,400,100,90,50,40,10,9,5,4,1};
        String[] romans={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
        int result=0,offset=0;
        while(offset<s.length())
        {
            for(int i=0;i<romans.length;i++)
            {
                if(s.startsWith(romans[i],offset))
                {
                    result+=vals[i];
                    offset+=romans[i].length();
                    break;
                }
            }
        }
        return result;