Leetcode: Integer to Roman

Given an integer, convert it to a roman numeral.



Input is guaranteed to be within the range from 1 to 3999.

一次过

 1 public class Solution {

 2     public String intToRoman(int num) {

 3         StringBuffer res = new StringBuffer();

 4         if (num > 3999 || num < 1) return res.toString();

 5         int copy = num;

 6         int thousand = copy / 1000; //# of thousand

 7         copy = copy - thousand * 1000;

 8         int hundred = copy / 100; //# of hundred

 9         copy = copy - hundred * 100;

10         int ten = copy / 10; //# of ten

11         copy = copy - ten * 10;

12         int one = copy / 1; //# of one

13         

14         if (thousand != 0) { //thousand

15             switch (thousand) {

16                 case 1: res.append("M"); break;

17                 case 2: res.append("MM"); break;

18                 case 3: res.append("MMM"); break;

19             }

20         }

21         

22         if (hundred != 0) { //thousand

23             switch (hundred) {

24                 case 1: res.append("C"); break;

25                 case 2: res.append("CC"); break;

26                 case 3: res.append("CCC"); break;

27                 case 4: res.append("CD"); break;

28                 case 5: res.append("D"); break;

29                 case 6: res.append("DC"); break;

30                 case 7: res.append("DCC"); break;

31                 case 8: res.append("DCCC"); break;

32                 case 9: res.append("CM"); break;

33             }

34         }

35         

36         if (ten != 0) { //thousand

37             switch (ten) {

38                 case 1: res.append("X"); break;

39                 case 2: res.append("XX"); break;

40                 case 3: res.append("XXX"); break;

41                 case 4: res.append("XL"); break;

42                 case 5: res.append("L"); break;

43                 case 6: res.append("LX"); break;

44                 case 7: res.append("LXX"); break;

45                 case 8: res.append("LXXX"); break;

46                 case 9: res.append("XC"); break;

47             }

48         }

49         

50         if (one != 0) { //thousand

51             switch (one) {

52                 case 1: res.append("I"); break;

53                 case 2: res.append("II"); break;

54                 case 3: res.append("III"); break;

55                 case 4: res.append("IV"); break;

56                 case 5: res.append("V"); break;

57                 case 6: res.append("VI"); break;

58                 case 7: res.append("VII"); break;

59                 case 8: res.append("VIII"); break;

60                 case 9: res.append("IX"); break;

61             }

62         }

63         return res.toString();

64     }

65 }

 这样做呢肯定有取巧的嫌疑，还是应该老老实实地按Roman Numerals的方法去构造，Code Ganker提供了一种不错的方法：

 1 public String intToRoman(int num) {

 2     //I 1

 3     //V 5

 4     //X 10

 5     //L 50

 6     //C 100

 7     //D 500

 8     //M 1,000

 9     if(num<1 || num>3999)

10         return "";

11     int digit = 1000;

12     ArrayList<Integer> digits = new ArrayList<Integer>();

13     while(digit>0)

14     {

15         digits.add(num/digit);

16         num %= digit;

17         digit /= 10;

18     }

19     StringBuilder res = new StringBuilder();

20     res.append(convert(digits.get(0),'M',' ', ' '));

21     res.append(convert(digits.get(1),'C','D', 'M'));

22     res.append(convert(digits.get(2),'X','L', 'C'));

23     res.append(convert(digits.get(3),'I','V', 'X'));

24     return res.toString();

25 }

26 public String convert(int digit, char one, char five, char ten)

27 {

28     StringBuilder res = new StringBuilder();

29     switch(digit)

30     {

31         case 9:

32             res.append(one);

33             res.append(ten);

34             break;

35         case 8:

36         case 7:

37         case 6:

38         case 5:

39             res.append(five);

40             for(int i=5;i<digit;i++)

41                 res.append(one);

42             break;

43         case 4:

44             res.append(one);

45             res.append(five);

46             break;   

47         case 3:

48         case 2:

49         case 1:

50             for(int i=0;i<digit;i++)

51                 res.append(one);

52             break;   

53         default:

54             break;

55     }

56     return res.toString();

57 }