LeetCode-in-All

416. Partition Equal Subset Sum

Medium

Given a non-empty array nums containing only positive integers, find if the array can be partitioned into two subsets such that the sum of elements in both subsets is equal.

Example 1:

Input: nums = [1,5,11,5]

Output: true

Explanation: The array can be partitioned as [1, 5, 5] and [11].

Example 2:

Input: nums = [1,2,3,5]

Output: false

Explanation: The array cannot be partitioned into equal sum subsets.

Constraints:

• 1 <= nums.length <= 200
• 1 <= nums[i] <= 100

Solution

defmodule Solution do
  @spec can_partition(nums :: [integer]) :: boolean
  def can_partition(nums) do
    sum = Enum.sum(nums)

    if rem(sum, 2) != 0 do
      false
    else
      target = div(sum, 2)

      for n <- nums, s <- target..n, reduce: %{0 => true} do
        dp -> Map.put(dp, s, Map.get(dp, s, false) || Map.get(dp, s - n, false))
      end
      |> Map.get(target)
    end
  end
end

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