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naveendk
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Beginner
Asked: 2025-02-23T02:24:55+00:00 In:

Product of Array Except Self – leet code

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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.

You must write an algorithm that runs in O(n) time and without using the division operation.

 

Example 1:

Input: nums = [1,2,3,4]
Output: [24,12,8,6]

Example 2:

Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]

 

Constraints:

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1 Answer

  1. nicko
    Beginner 
    def productExceptSelf(nums):
n = len(nums)
answer = [1] * n

# Calculate prefix product
prefix = 1
for i in range(n):
answer[i] = prefix
prefix *= nums[i]

# Calculate suffix product and multiply with prefix
suffix = 1
for i in range(n - 1, -1, -1):
answer[i] *= suffix
suffix *= nums[i]

return answer

    Explanation:

    1. First loop: Compute prefix product for each element (product of all elements before i).
    2. Second loop: Compute suffix product (product of all elements after i) and multiply with prefix to get the final result.
    3. This way, for each i, we get the product of all elements except nums[i].

    ✅ Time Complexity: O(n)
    ✅ Space Complexity: O(1) extra space (ignoring output array)