I have designed this by using the stack data structure (similar to balanced parentheses problem) checking if the previous element is decreasing the number or not.
package test;
import main.algorithms.RomanConversion;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
public class RomanConversionTest {
RomanConversion romanConversion;
@Before
public void setUp(){
romanConversion = new RomanConversion();
}
@Test
public void testRomanConversion(){
Assert.assertEquals(154, romanConversion.convert("CLIV"));
Assert.assertEquals(101, romanConversion.convert("CI"));
Assert.assertEquals(43, romanConversion.convert("XLIII"));
}
}
package main.algorithms;
import java.util.HashMap;
import java.util.Stack;
public class RomanConversion {
public HashMap createMap(){
HashMap<String, Integer> romanMap = new HashMap<>();
romanMap.put("I" , 1);
romanMap.put("IV",4);
romanMap.put("V" ,5);
romanMap.put("IX",9);
romanMap.put("X" ,10);
romanMap.put("XL",40);
romanMap.put("L" ,50);
romanMap.put("XC",90);
romanMap.put("C" ,100);
romanMap.put("CD",400);
romanMap.put("D" ,500);
romanMap.put("CM",900);
romanMap.put("M" ,1000);
return romanMap;
}
public int convert(String letter) {
int result=0;
HashMap<String, Integer> map = new HashMap<>();
map = createMap();
String str;
char[] array = letter.toCharArray();
Stack<Character> stack = new Stack<>();
for(char c: array){
if(stack.isEmpty()){
result += map.get(String.valueOf(c));
stack.push(c);
}else{
char lastElement= stack.peek();
if(map.containsKey(lastElement+""+c)) {
result -= map.get(String.valueOf(lastElement));
result += map.get(String.valueOf(lastElement) + String.valueOf(c));
stack.push(c);
}else{
result += map.get(String.valueOf(c));
stack.push(c);
}
}
}
return result;
}
}
