adding algo

src/my_project/interviews/top_150_questions_round_20/plus_one.py

@@ -0,0 +1,20 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class Solution:
+    def plusOne(self, digits: List[int]) -> List[int]:
+
+        len_digits = len(digits)
+
+        for i in range(len_digits - 1, -1, -1):
+
+            if digits[i] != 9:
+                digits[i] += 1
+                break 
+            else: 
+                digits[i] = 0
+
+        if digits[0] == 0:
+            return [1] + digits
+        else: 
+            return digits

tests/test_150_questions_round_20/test_plus_one_round_20.py

@@ -0,0 +1,19 @@
+import unittest
+from src.my_project.interviews.top_150_questions_round_20\
+.plus_one import Solution
+
+class PlusOneTestCase(unittest.TestCase):
+
+    def test_leading_one(self):
+        solution = Solution()
+        output = solution.plusOne(digits=[9])
+        target = [1, 0] 
+        for k, v in enumerate(target):
+            self.assertEqual(v, output[k])
+
+    def test_no_leading_one(self):
+        solution = Solution()
+        output = solution.plusOne(digits=[1, 2])
+        target = [1, 3] 
+        for k, v in enumerate(target):
+            self.assertEqual(v, output[k])