Add additional solutions for neetcode: products of array except self

neetcode/arrays/products_of_array_except_self/products_of_array_except_self.py

@@ -3,6 +3,8 @@ import pytest
 
 
 class Solution:
+    """Bruteforce solution (4 hints)"""
+
     def productExceptSelf(self, nums: List[int]) -> List[int]:
         if not nums:
             return []
@@ -25,15 +27,57 @@ class Solution:
         return res
 
 
+class SolutionUnoptimal:
+    """Unoptimal prefix-postfix solution"""
+
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        prefixes: List[int] = [1] * len(nums)
+        postfixes: List[int] = [1] * len(nums)
+        res: List[int] = [1] * len(nums)
+        prefix, postfix = 1, 1
+        for num_index in range(0, len(nums)):
+            prefixes[num_index] = prefix * nums[num_index]
+            prefix = prefixes[num_index]
+        for num_index in range(len(nums) - 1, -1, -1):
+            postfixes[num_index] = postfix * nums[num_index]
+            postfix = postfixes[num_index]
+        for i in range(0, len(res)):
+            if i == 0:
+                res[i] = 1 * postfixes[i + 1]
+                continue
+            if i == len(res) - 1:
+                res[i] = prefixes[i - 1] * 1
+                continue
+            res[i] = prefixes[i - 1] * postfixes[i + 1]
+        return res
+
+
+class SolutionOptimal:
+    """Optimal prefix-postfix solution"""
+
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        prefix: int = 1
+        res: List[int] = [1] * len(nums)
+        # Left -> Right
+        for i in range(0, len(nums)):
+            res[i] = prefix
+            prefix = nums[i] * prefix
+        # Right -> Left
+        postfix: int = 1
+        for i in range(len(nums) - 1, -1, -1):
+            res[i] = postfix * res[i]
+            postfix = nums[i] * postfix
+        return res
+
+
 @pytest.mark.parametrize(
     "input_value, expected_value",
     [
         ([1, 2, 4, 6], [48, 24, 12, 8]),
         ([-1, 0, 1, 2, 3], [0, -6, 0, 0, 0]),
-        ([], []),
         ([-1, 1, 0, -3, 3], [0, 0, 9, 0, 0]),
     ],
 )
 def test_solution(input_value, expected_value):
-    s = Solution()
+    s = SolutionOptimal()
     assert s.productExceptSelf(nums=input_value) == expected_value