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RomanToInteger.java

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package Conversions;

import java.util.*;

public class RomanToInteger {

private static Map<Character, Integer> map = new HashMap<Character, Integer>() {

/**

*

*/

private static final long serialVersionUID = 87605733047260530L;

{

put('I', 1);

put('V', 5);

put('X', 10);

put('L', 50);

put('C', 100);

put('D', 500);

put('M', 1000);

}};

//Roman Number = Roman Numerals

/**

* This function convert Roman number into Integer

*

* @param A Roman number string

* @return integer

*/

public static int romanToInt(String A) {

char prev = ' ';

int sum = 0;

int newPrev = 0;

for (int i = A.length() - 1; i >= 0; i--) {

char c = A.charAt(i);

if (prev != ' ') {

// checking current Number greater then previous or not

newPrev = map.get(prev) > newPrev ? map.get(prev) : newPrev;

}

int currentNum = map.get(c);

// if current number greater then prev max previous then add

if (currentNum >= newPrev) {

sum += currentNum;

} else {

// subtract upcoming number until upcoming number not greater then prev max

sum -= currentNum;

}

prev = c;

}

return sum;

}

public static void main(String[] args) {

int sum = romanToInt("MDCCCIV");

System.out.println(sum);

}

}