Roman Numeral Chart
V:5 X:10 L:50 C:100 D:500 M:1000
规则：
1. 重复次数表示该数的倍数
2. 右加左减：
较大的罗马数字右边记上较小的罗马数字，表示大数字加小数字
较小的罗马数字右边记上较大的罗马数字，表示大数字减小数字
左减的数字有限制，仅限于I, X, C
左减时不可跨越一个位数。如，99不可以用IC(100 - 1)表示，而是XCIX(100 - 10 + 10 - 1)
左减数字必需为一位
右加数字不可连续超过三位
Roman to Integer
Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.
基本思路是每次比较当前字母和它下一个字母，如果是increasing order，说明当前字母的符号是减号，如果是decreasing order，说明当前字母的符号是加号。
1 class Solution(object): 2 def romanToInt(self, s): 3 """ 4 :type s: str 5 :rtype: int 6 """ 7 result = 0 8 my_map = {'I':1, 'V':5, 'X':10,'L':50, 'C':100, 'D':500, 'M':1000} 9 for i in range(len(s) - 1): 10 if (my_map[s[i]] - my_map[s[i + 1]]) >= 0: 11 result += my_map[s[i]] 12 else: 13 result -= my_map[s[i]] 14 result += my_map[s[len(s) - 1]] 15 return result
Integer to Roman
根据规则，可以用递归和非递归的方法解答。
注意到规则，跨越的位数不可超过一位。
1 public class Solution { 2 public String intToRoman(int num) { 3 if (num >= 1000) { return "M" + intToRoman(num - 1000); } 4 if (num >= 900) { return "CM" + intToRoman(num - 900); } 5 if (num >= 500) { return "D" + intToRoman(num - 500); } 6 if (num >= 400) { return "CD" + intToRoman(num - 400); } 7 if (num >= 100) { return "C" + intToRoman(num - 100); } 8 if (num >= 90) { return "XC" + intToRoman(num - 90); } 9 if (num >= 50) { return "L" + intToRoman(num - 50); } 10 if (num >= 40) { return "XL" + intToRoman(num - 40); } 11 if (num >= 10) { return "X" + intToRoman(num - 10); } 12 if (num >= 9) { return "IX" + intToRoman(num - 9); } 13 if (num >= 5) { return "V" + intToRoman(num - 5); } 14 if (num >= 4) { return "IV" + intToRoman(num - 4); } 15 if (num >= 1) { return "I" + intToRoman(num - 1); } 16 return ""; 17 } 18 }
循环改为非递归
1 public class Solution { 2 public String intToRoman(int num) { 3 String result = ""; 4 String [] symbol = {"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"}; 5 int [] value = {1000,900,500,400, 100, 90, 50, 40, 10, 9, 5, 4, 1}; 6 for(int i=0;num!=0;i++){ 7 while(num >= value[i]){ 8 num -= value[i]; 9 result += symbol[i]; 10 } 11 } 12 return result; 13 } 14 }