LeetCode in Elixir
152. Maximum Product Subarray
Medium
Given an integer array nums, find a contiguous non-empty subarray within the array that has the largest product, and return the product.
The test cases are generated so that the answer will fit in a 32-bit integer.
A subarray is a contiguous subsequence of the array.
Example 1:
Input: nums = [2,3,-2,4]
Output: 6
Explanation: [2,3] has the largest product 6.
Example 2:
Input: nums = [-2,0,-1]
Output: 0
Explanation: The result cannot be 2, because [-2,-1] is not a subarray.
Constraints:
1 <= nums.length <= 2 * 104-10 <= nums[i] <= 10- The product of any prefix or suffix of
numsis guaranteed to fit in a 32-bit integer.
Solution
defmodule Solution do
@spec max_product(nums :: [integer]) :: integer
def max_product(nums) do
nums
|> Stream.chunk_by(& &1 == 0)
|> Stream.map(&max_prod/1)
|> Enum.max()
end
defp max_prod([0 | _]), do: 0
defp max_prod([n]), do: n
defp max_prod(chunk) do
prod = Enum.product(chunk)
max(
div_till_pos(prod, chunk),
div_till_pos(prod, Enum.reverse(chunk))
)
end
defp div_till_pos(prod, _) when prod > 0, do: prod
defp div_till_pos(prod, [n | t]), do: prod |> div(n) |> div_till_pos(t)
end