public int romanToInt(String s) {

//https://leetcode.com/problems/roman-to-integer/

int[] flags = new int[] {1, 4, 5, 9, 10, 40, 50, 90, 100, 400, 500, 900, 1000};

String[] romans = new String[] {"I", "IV", "V", "IX", "X", "XL", "L", "XC", "C", "CD", "D", "CM", "M"};

int i = romans.length - 1;

int ans = 0;

int j = 0; // Points to the start of target string

// Just replace whenever it sees a combination of romans elements

while (j < s.length()) {

if (romans[i].length() == 1 && s.substring(j, j+1).equals(romans[i])) {

ans = ans + flags[i];

j += 1;

i += 1;

} else if (j < s.length()-1 && romans[i].length() == 2 && s.substring(j, j+2).equals(romans[i])) {

ans = ans + flags[i];

j += 2;

i += 1;

}

i--;

}

return ans;

}

public static void main(String[] args) {

Roman2Integer r = new Roman2Integer();

System.out.println("Should be 1: " + r.romanToInt("I"));

System.out.println("Should be 9: " + r.romanToInt("IX"));

System.out.println("Should be 41: " + r.romanToInt("XLI"));

System.out.println("Should be 2943: " + r.romanToInt("MMCMXLIII"));

}