added Roman to Integer Solution in String Problems

Author: AyushJoshi2001

Topic/Solution/romanToInt.java

@@ -0,0 +1,26 @@
+class Solution {
+    public int romanToInt(String s) {
+        int ans = 0;
+        int n = s.length();
+
+        HashMap<Character, Integer> 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);
+
+        for(int i=0; i<n; i++){
+            if((i!=n-1) && (map.get(s.charAt(i)) < map.get(s.charAt(i+1)))){
+                ans -= map.get(s.charAt(i));
+            }
+            else{
+                ans += map.get(s.charAt(i));
+            }
+        }
+
+        return ans;
+    }
+}