add integer to roman function (#4050)

* add integer to roman function

simply added fastest method i found.

* Rename roman_to_integer.py to roman_numerals.py

* Update roman_numerals.py

* Update roman_numerals.py

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

conversions/roman_numerals.py

@@ -21,6 +21,38 @@ def roman_to_int(roman: str) -> int:
     return total
 
 
+def int_to_roman(number: int) -> str:
+    """
+    Given a integer, convert it to an roman numeral.
+    https://en.wikipedia.org/wiki/Roman_numerals
+    >>> tests = {"III": 3, "CLIV": 154, "MIX": 1009, "MMD": 2500, "MMMCMXCIX": 3999}
+    >>> all(int_to_roman(value) == key for key, value in tests.items())
+    True
+    """
+    ROMAN = [
+        (1000, "M"),
+        (900, "CM"),
+        (500, "D"),
+        (400, "CD"),
+        (100, "C"),
+        (90, "XC"),
+        (50, "L"),
+        (40, "XL"),
+        (10, "X"),
+        (9, "IX"),
+        (5, "V"),
+        (4, "IV"),
+        (1, "I"),
+    ]
+    result = []
+    for (arabic, roman) in ROMAN:
+        (factor, number) = divmod(number, arabic)
+        result.append(roman * factor)
+        if number == 0:
+            break
+    return "".join(result)
+
+
 if __name__ == "__main__":
     import doctest