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find_triangular_sum.exs
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find_triangular_sum.exs
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# https://leetcode.com/problems/find-triangular-sum-of-an-array/description/
# 2221. Find Triangular Sum of an Array
defmodule Solution do
@spec triangular_sum(nums :: [integer]) :: integer
def triangular_sum([res]), do: res
def triangular_sum(nums) do
triangular_sum(triangle_round(nums))
end
defp triangle_round(list) do
list
|> Enum.chunk_every(2, 1, :discard)
|> Enum.map(fn [n1, n2] ->
rem(n1 + n2, 10)
end)
end
def triangular_sum_ii(nums) do
len = Enum.count(nums) - 1
nums
|> Enum.reduce({0, 1, 0}, fn num, {i, mCk, res} ->
{i + 1, div(mCk*(len - i), (i + 1)), rem(res + num*mCk, 10)}
end)
|> elem(2)
end
end
IO.inspect("Find Triangular Sum of an Array (recursive)")
IO.inspect(Solution.triangular_sum([1,2,3,4,5]))
# Output: 8
IO.inspect(Solution.triangular_sum([5]))
# Output: 5
IO.inspect("Find Triangular Sum of an Array (Pascal Triangle)")
IO.inspect(Solution.triangular_sum_ii([1,2,3,4,5]))
# Output: 8
IO.inspect(Solution.triangular_sum_ii([5]))
# Output: 5