add solution: product-of-array-except-self

Author: dusunax

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

@@ -0,0 +1,34 @@
+'''
+# 238. Product of Array Except Self
+
+use prefix and suffix to calculate the product of the array, except self.
+
+## Time and Space Complexity
+
+```
+TC: O(n)
+SC: O(n)
+```
+
+### TC is O(n):
+- iterating through the list twice, to calculate both prefix and suffix products. = O(n)
+
+### SC is O(n):
+- storing the prefix and suffix in the answer list. = O(n)
+'''
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        answer = [1] * n
+
+        # prefix
+        for i in range(1, n):
+            answer[i] *= nums[i - 1] * answer[i - 1]
+
+        # suffix
+        suffix_product = 1
+        for i in range(n - 1, -1, -1):
+            answer[i] *= suffix_product
+            suffix_product *= nums[i]
+
+        return answer