Add optimized and standard implementations for Product of Array Except Self algorithm

data_structures/arrays/ProductOfArrayExceptSelf.py

@@ -0,0 +1,95 @@
+from typing import List
+import doctest
+
+
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        """
+        Given an integer array nums, return an array answer such that
+        answer[i] is equal to the product of all the elements of nums except nums[i].
+
+        The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
+
+        This solution runs in O(n) time and O(1) extra space (excluding output),
+        without using division.
+
+        >>> Solution().productExceptSelf([1, 2, 3, 4])
+        [24, 12, 8, 6]
+        >>> Solution().productExceptSelf([-1, 1, 0, -3, 3])
+        [0, 0, 9, 0, 0]
+        >>> Solution().productExceptSelf([0, 0, 0])
+        [0, 0, 0]
+        >>> Solution().productExceptSelf([0, 1, 2, 3])
+        [6, 0, 0, 0]
+        >>> Solution().productExceptSelf([0, 0, 1])
+        [0, 0, 0]
+        >>> Solution().productExceptSelf([-1, -2, -3])
+        [6, 3, 2]
+        >>> Solution().productExceptSelf([1, 2])
+        [2, 1]
+        >>> Solution().productExceptSelf([1, 1, 1])
+        [1, 1, 1]
+        >>> Solution().productExceptSelf([-30, 30, -30, 30])
+        [-27000, 27000, -27000, 27000]
+        >>> Solution().productExceptSelf([5, 0, 0, 5])
+        [0, 0, 0, 0]
+        """
+        n = len(nums)
+        answer = [1] * n
+
+        # Left pass: Compute prefix products
+        left_product = 1
+        for i in range(n):
+            answer[i] *= left_product
+            left_product *= nums[i]
+
+        # Right pass: Compute suffix products and multiply into answer
+        right_product = 1
+        for i in range(n - 1, -1, -1):
+            answer[i] *= right_product
+            right_product *= nums[i]
+
+        return answer
+
+
+# #optimized Answer
+# class Solution(object):
+#     def productExceptSelf(self, nums):
+#         m = 1
+#         z = 0
+#         for i in nums:
+#             if i !=0:
+#                 m*= i
+#             else:
+#                 z+=1
+
+#         if z==1:
+#             return [m if i==0 else 0 for i in nums]
+#         if z>1:
+#             return [0]*len(nums)
+#         return [m//i for i in nums]
+
+
+if __name__ == "__main__":
+    # Run doctests
+    doctest.testmod()
+
+    # Additional manual execution example
+    sol = Solution()
+    test_cases = [
+        [1, 2, 3, 4],
+        [-1, 1, 0, -3, 3],
+        [0, 0, 0],
+        [0, 1, 2, 3],
+        [0, 0, 1],
+        [-1, -2, -3],
+        [1, 2],
+        [1, 1, 1],
+        [-30, 30, -30, 30],
+        [5, 0, 0, 5],
+    ]
+
+    print("\nRunning additional test cases:")
+    for case in test_cases:
+        result = sol.productExceptSelf(case)
+        print(f"Input: {case} -> Output: {result}")