Create roman_to_integer.py (#1636)

* added roman to integer conversion (LeetCode No. 13)

* updated directory to include Roman to Integer

* Delete DIRECTORY.md

* Update roman_to_integer.py

Co-authored-by: Christian Clauss <cclauss@me.com>

conversions/roman_to_integer.py

@@ -0,0 +1,27 @@
+def roman_to_int(roman: str) -> int:
+    """
+    LeetCode No. 13 Roman to Integer
+    Given a roman numeral, convert it to an integer.
+    Input is guaranteed to be within the range from 1 to 3999.
+    https://en.wikipedia.org/wiki/Roman_numerals
+    >>> tests = {"III": 3, "CLIV": 154, "MIX": 1009, "MMD": 2500, "MMMCMXCIX": 3999}
+    >>> all(roman_to_int(key) == value for key, value in tests.items())
+    True
+    """
+    vals = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
+    total = 0
+    place = 0
+    while place < len(roman):
+        if (place + 1 < len(roman)) and (vals[roman[place]] < vals[roman[place + 1]]):
+            total += vals[roman[place + 1]] - vals[roman[place]]
+            place += 2
+        else:
+            total += vals[roman[place]]
+            place += 1
+    return total
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()