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How do you compute the product of an array except self without division?

Q: How do you compute the product of an array except self without division?

**Intuition.** output[i] is "everything to the left of i" times "everything to the right of i". Compute those two running products in two passes — no division needed (which also dodges the divide-by-zero problem when the array contains a 0). pass 1 → prefix products (product of everything to the left) 1 <text x="190"

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Prefix then suffix

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def product_except_self(nums):
    n = len(nums)
    out = [1] * n
    prefix = 1
    for i in range(n):
        out[i] = prefix
        prefix *= nums[i]
    suffix = 1
    for i in range(n - 1, -1, -1):
        out[i] *= suffix
        suffix *= nums[i]
    return out


# --- demo ---
print(product_except_self([1, 2, 3, 4]))   # [24, 12, 8, 6]

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