feat: add integer_to_roman algorithm with doctests

Author: NA-V10

strings/integer_to_roman.py

@@ -0,0 +1,51 @@
+def integer_to_roman(n: int) -> str:
+    """
+    Convert an integer to a Roman numeral.
+
+    Examples:
+    >>> integer_to_roman(1)
+    'I'
+    >>> integer_to_roman(4)
+    'IV'
+    >>> integer_to_roman(9)
+    'IX'
+    >>> integer_to_roman(58)
+    'LVIII'
+    >>> integer_to_roman(1994)
+    'MCMXCIV'
+    >>> integer_to_roman(0)
+    Traceback (most recent call last):
+        ...
+    ValueError: number must be between 1 and 3999
+    """
+    if not (1 <= n <= 3999):
+        raise ValueError("number must be between 1 and 3999")
+
+    symbols = [
+        (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 value, numeral in symbols:
+        while n >= value:
+            result.append(numeral)
+            n -= value
+
+    return "".join(result)
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()