product of array except self solution

Author: yerim01

product-of-array-except-self/yerim01.py

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+# Goal: Return an array answer that product of all elements except nums[i].
+#
+# Approach:
+# Use prefix&suffix arrays to store cumulative products
+# - prefix: product of elements to the left of i
+# - suffix: product of elements to the right of i
+# Calculate the result[i] by multipying prefix[i] and suffix[i]
+#
+# Time Complexity: O(n)
+# - We Iterate the array to compute prefix, suffix and result.
+# Space Complexity: O(n)
+# - We use extra arrays for prefix&suffix.
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+
+        prefix = [1] * n
+        suffix = [1] * n
+        result = [1] * n
+
+        for i in range(1, n):
+            prefix[i] = prefix[i-1] * nums[i-1]
+        
+        for i in range(n-2, -1, -1):
+            suffix[i] = suffix[i+1] * nums[i+1]
+        
+        for i in range(len(nums)):
+            result[i] = prefix[i] * suffix[i]
+        
+        return result