Product of Array Except Self Solution

Author: jungsiroo

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

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+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        # Solution 1 :모든 수를 미리 곱해두기
+        # 0을 포함한다면 미리 0의 개수를 체크해두기
+
+        n = len(nums)
+        ret = [0 for _ in range(n)]
+        """
+        all_product = 1
+        non_zero_product = 1
+        zero_cnt = 0
+
+        for x in nums:
+            all_product *= x
+
+            if x == 0: 
+                zero_cnt += 1
+            else:
+                non_zero_product *= x
+
+        if zero_cnt > 1:
+            return ret
+
+        for i in range(n):
+            if nums[i] == 0:
+                ans = non_zero_product
+            else:
+                ans = all_product // nums[i]
+            ret[i] = ans
+        return ret
+        """
+
+        # Solution 2 : w/o division
+        # prefix sum과 같이 풀이 진행
+        # Tc : O(n) / Sc : O(n) - no extra memory
+
+        prefix_pr, postfix_pr = 1, 1
+        for i in range(n):
+            ret[i] = prefix_pr
+            prefix_pr *= nums[i]
+        for i in range(n-1, -1, -1):
+            ret[i] *= postfix_pr
+            postfix_pr *= nums[i]
+        return ret
+            
+