chore(Python): add roman number to int (#1084)

Co-authored-by: Humberto Harris <hharris@techgenies.com>

algorithms/Python/README.md

@@ -66,6 +66,7 @@
 - [Add String](strings/add_string.py)
 - [Rabin Karp algorithm](strings/rabin-karp-algorithm.py)
 - [Find all permutations](strings/find_all_permutations.py)
+- [Roman to Int](strings/roman-to-int.py)
 
 ## Dynamic Programming
 - [Print Fibonacci Series Up To N-th Term](dynamic_programming/fibonacci_series.py)

algorithms/Python/strings/roman-to-int.py

@@ -0,0 +1,41 @@
+"""
+This program converts a string that represents a valid roman number to its decimal equivalent.
+If the string is not a valid roman number, raises a ValueError exception.
+Time Complexity : O(n)
+Space Complexity : O(1)
+"""
+
+equivalence = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
+
+def is_valid_roman_string(roman_number: str) -> bool:
+    """Returns True if all characters of the given string are valid roman numbers"""
+    return set(roman_number).issubset(equivalence.keys())
+
+
+def conversion(roman_number: str) -> int:
+    """Traverses a given roman number and returns its decimal equivalent"""
+    digits = len(roman_number)
+    result = 0
+
+    for i, char in enumerate(roman_number):
+        if i < digits - 1 and equivalence[char] < equivalence[roman_number[i + 1]]:
+            result -= equivalence[char]
+        else:
+            result += equivalence[char]
+
+    return result
+
+
+def roman_to_int(roman_number: str) -> int | ValueError:
+    """Main function"""
+    if not is_valid_roman_string(roman_number):
+        raise ValueError(f'The string must contain only valid roman numbers: {equivalence.keys()}')
+
+    return conversion(roman_number)
+
+
+if __name__ == '__main__':
+    print(roman_to_int('MCMXCIV'))
+    # 1994
+    print(roman_to_int('abc'))
+    # ValueError: The string must contain only valid roman numbers: dict_keys(['I', 'V', 'X', 'L', 'C', 'D', 'M'])