Add problem 43 - Multiply Strings

Author: anirudhology

problems/math/multiply_strings.py

@@ -0,0 +1,23 @@
+class MultiplyStrings:
+    @staticmethod
+    def multiply(num1: str, num2: str) -> str:
+        # Special case
+        if num1 == '0' or num2 == '0':
+            return '0'
+        # Lengths of two strings
+        m, n = len(num1), len(num2)
+        # List to store the products
+        products = [0] * (m + n - 1)
+        # Process the strings
+        for i in range(m):
+            for j in range(n):
+                products[i + j] += (ord(num1[i]) - ord('0')) * (ord(num2[j]) - ord('0'))
+        # Process the products array further
+        for i in range(len(products) - 1, 0, -1):
+            products[i - 1] += products[i] // 10
+            products[i] %= 10
+        # String for the final result
+        output = ''
+        for i in products:
+            output += str(i)
+        return output

tests/math/multiply_strings_test.py

@@ -0,0 +1,25 @@
+import unittest
+
+from problems.math.multiply_strings import MultiplyStrings
+
+
+class TestMultiplyStrings(unittest.TestCase):
+
+    def setUp(self):
+        self.multiply_strings = MultiplyStrings()
+
+    def test_multiply_with_zero(self):
+        self.assertEqual(self.multiply_strings.multiply("0", "1234"), "0")
+        self.assertEqual(self.multiply_strings.multiply("5678", "0"), "0")
+
+    def test_multiply_single_digit_numbers(self):
+        self.assertEqual(self.multiply_strings.multiply("3", "3"), "9")
+        self.assertEqual(self.multiply_strings.multiply("5", "9"), "45")
+
+    def test_multiply_multi_digit_numbers(self):
+        self.assertEqual(self.multiply_strings.multiply("123", "456"), "56088")
+        self.assertEqual(self.multiply_strings.multiply("999", "999"), "998001")
+
+
+if __name__ == '__main__':
+    unittest.main()