[LintCode] Roman to Integer
Given a roman numeral, convert it to an integer.
The answer is guaranteed to be within the range from 1 to 3999.
Clarification
Example
IV -> 4
XII -> 12
XXI -> 21
XCIX -> 99
Observation: if s.charAt(i) > s.charAt(i - 1), it means we need to subtract the mapped value of s.charAt(i - 1) from the mapped value of s.charAt(i).
Based on this observation, the following algorithm is developed.
1. init result to m.get(s.charAt(length - 1)), the mapped value of the last character.
2. starting from the 2nd last character, iterate through the string from right to left; if the current character's mapped value is smaller than
its right neighbor's, subtract this mapped value from the result; if not, add this mapped value to the result.
1 public class Solution { 2 public int romanToInt(String s) { 3 if (s == null || s.length()==0) { 4 return 0; 5 } 6 Map<Character, Integer> m = new HashMap<Character, Integer>(); 7 m.put('I', 1); 8 m.put('V', 5); 9 m.put('X', 10); 10 m.put('L', 50); 11 m.put('C', 100); 12 m.put('D', 500); 13 m.put('M', 1000); 14 15 int length = s.length(); 16 int result = m.get(s.charAt(length - 1)); 17 for (int i = length - 2; i >= 0; i--) { 18 if (m.get(s.charAt(i + 1)) <= m.get(s.charAt(i))) { 19 result += m.get(s.charAt(i)); 20 } else { 21 result -= m.get(s.charAt(i)); 22 } 23 } 24 return result; 25 } 26 }
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Integer to Roman
