Merge pull request TheAlgorithms#720 from pandeyarun709/TheAlgo

Add Roman To Integer conversion

Author: yanglbme

Conversions/RomanToInteger.java

@@ -0,0 +1,56 @@
+import java.util.*;
+
+public class RomanToInteger {
+
+    private static Map<Character, Integer> map = new HashMap<>() {{
+        put('I', 1);
+        put('V', 5);
+        put('X', 10);
+        put('L', 50);
+        put('C', 100);
+        put('D', 500);
+        put('M', 1000);
+    }};
+
+    /**
+     * 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);
+    }
+}