Add a solution to product-of-array-except-self problem.

Author: KyrieJ95

product-of-array-except-self/joon.py

@@ -0,0 +1,28 @@
+from typing import List
+from functools import reduce
+
+
+class Solution:
+    # Time: O(n)
+    # Space: O(n)
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        size: int = len(nums)
+        if size == 1:
+            return [1]
+        # 1. Cut the array at the middle.
+        # Time: O(1)
+        # Space: O(n)
+        indexToCut: int = len(nums) // 2
+        left: List[int] = nums[0:indexToCut]
+        right: List[int] = nums[indexToCut:size]
+
+        # 2. Divide, conquer, and merge. But no benefit in complexity.
+        # Time: O(n)
+        # Space: O(n)
+        return self.multiplyToAll(self.productExceptSelf(left), self.calculateProductAll(right)) + self.multiplyToAll(self.productExceptSelf(right), self.calculateProductAll(left))
+
+    def calculateProductAll(self, nums: List[int]) -> int:
+        return reduce(lambda x, y: x * y, nums)
+
+    def multiplyToAll(self, nums: List[int], multiplier: int) -> List[int]:
+        return list(map(lambda num: multiplier * num, nums))