add: Luhn algorithm

Luhn algorithm is mostly used for validation.

Author: NitkarshChourasia

luhn_algorithm_for_credit_card_validation.py

@@ -0,0 +1,39 @@
+"""
+The Luhn Algorithm is widely used for error-checking in various applications, such as verifying credit card numbers.
+
+By building this project, you'll gain experience working with numerical computations and string manipulation.
+
+"""
+
+
+def verify_card_number(card_number):
+    sum_of_odd_digits = 0
+    card_number_reversed = card_number[::-1]
+    odd_digits = card_number_reversed[::2]
+
+    for digit in odd_digits:
+        sum_of_odd_digits += int(digit)
+
+    sum_of_even_digits = 0
+    even_digits = card_number_reversed[1::2]
+    for digit in even_digits:
+        number = int(digit) * 2
+        if number >= 10:
+            number = (number // 10) + (number % 10)
+        sum_of_even_digits += number
+    total = sum_of_odd_digits + sum_of_even_digits
+    return total % 10 == 0
+
+
+def main():
+    card_number = "4111-1111-4555-1142"
+    card_translation = str.maketrans({"-": "", " ": ""})
+    translated_card_number = card_number.translate(card_translation)
+
+    if verify_card_number(translated_card_number):
+        print("VALID!")
+    else:
+        print("INVALID!")
+
+
+main()