Roman to Integer

Question: Given String value of a Roman numeral, compute and return the integer equivalent. Find the full question here.

Approach 1: As usual let’s start with the simplest solution —

class Solution {
//Runtime: 36ms
//Memory usage: 39MB 
 Map<Character, Integer> map = new HashMap();
 
 private void setMap(){
 map = new HashMap();
 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);
 }
 public int romanToInt(String s) {
 setMap();
 char[] roman = s.toCharArray();
 int finalInt = 0;
 for(int i = 0; i<roman.length-1; i++) {
 if(map.get(roman[i])>=map.get(roman[i+1])) {
 finalInt+=map.get(roman[i]);
 }else {
 finalInt-=map.get(roman[i]);
 }
 }
 return finalInt+map.get(roman[roman.length-1]);
 }
}

Using a HashMap for lookup and following the instructions in the question was the easiest way to tackle the problem. There’s definitely a lot of scope for improvement, which we’ll look at in a future post shared here. Until then…

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Cheers & Chao!