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 }