import java.util.HashMap;

/*

* A number written in Arabic numerals can be broken into digits.

* For example, 1903 is composed of 1 (one thousand), 9 (nine hundreds), 0 (zero tens), and 3 (three units).

* To write the Roman numeral, each of the non-zero digits should be treated separately.

* In the above example, 1,000 = M, 900 = CM, and 3 = III. Therefore, 1903 = MCMIII.[4]

* The symbols "I", "X", "C", and "M" can be repeated three times in succession, but no more.

* (They may appear more than three times if they appear non-sequentially, such as XXXIX.)

* "D", "L", and "V" can never be repeated.[5][6]

* "I" can be subtracted from "V" and "X" only.

* "X" can be subtracted from "L" and "C" only.

* "C" can be subtracted from "D" and "M" only.

* "V", "L", and "D" can never be subtracted[6]

* Only one small-value symbol may be subtracted from any large-value symbol.[7]

* */

/*

* I = 1

* V = 5

* X = 10

* L = 50

* C = 100

* D = 500

* M = 1000

*

*/

public class RomanToInteger {

public int romanToInt(String s) {

HashMap<Character,Integer> map = new HashMap<Character, Integer>();

map.put('I', 1);

map.put('V', 5);

map.put('X',10);

map.put('L',50);

map.put('C', 100);

map.put('D', 500);

map.put('M', 1000);

int len = s.length();

char[] arr = s.toCharArray();

int result = map.get(arr[len - 1]);

int value = result;

int post;

for (int i = len - 2; i >= 0; i--) {

post = value;

value = map.get(arr[i]);

if (value < post) {

result -= value;

}

else {

result += value;

}

}

return result;

}

}