python: add problem 43 and unittest

Author: supercoderhawk

Python/sln_1_100/solution_41_50.py

@@ -1,6 +1,23 @@
 # -*- coding: UTF-8 -*-
 
 class Solution_41_50:
+    def multiply(self, num1: str, num2: str) -> str:
+        """
+        43
+        Given two non-negative integers num1 and num2 represented as strings,
+        return the product of num1 and num2, also represented as a string.
+        :param num1:
+        :param num2:
+        :return:
+        """
+        mul_ret = 0
+        for idx1, digit1 in enumerate(num1[::-1]):
+            val1 = (ord(digit1) - ord('0')) * 10 ** idx1
+            for idx2, digit2 in enumerate(num2[::-1]):
+                val2 = (ord(digit2) - ord('0')) * 10 ** idx2
+                mul_ret += val1 * val2
+        return str(mul_ret)
+
     def permute(self, nums):
         """
         problem 46

Python/sln_1_100/test_solution_41_50.py

@@ -7,6 +7,11 @@ class TestSolution_41_50(TestCase):
     def setUp(self):
         self.sln = Solution_41_50()
 
+    def test_multiply(self):
+        self.assertEqual(self.sln.multiply('3', '2'), '6')
+        self.assertEqual(self.sln.multiply('123', '456'), '56088')
+        self.assertEqual(self.sln.multiply('123', '0'), '0')
+
     def test_permute(self):
         a = [1, 2, 3]
         b = [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]