LeetCode-in-All

739. Daily Temperatures

Medium

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

Example 1:

Input: temperatures = [73,74,75,71,69,72,76,73]

Output: [1,1,4,2,1,1,0,0]

Example 2:

Input: temperatures = [30,40,50,60]

Output: [1,1,1,0]

Example 3:

Input: temperatures = [30,60,90]

Output: [1,1,0]

Constraints:

Solution

defmodule Solution do
  @spec daily_temperatures(temp :: [integer]) :: [integer]
  def daily_temperatures(temp) do
    Enum.reverse(temp)
    |> Enum.with_index()
    |> Enum.map_reduce([], &do_map_reduce/2)
    |> elem(0)
    |> Enum.reverse()
  end

  defp do_map_reduce({x, i}, [{y, j} | tail]) when x >= y do
    do_map_reduce({x, i}, tail)
  end
  defp do_map_reduce({x, i}, [{y, j} | tail]) do
    {i - j, [{x, i}, {y, j} | tail]}
  end
  defp do_map_reduce({x, i}, []) do
    {0, [{x, i}]}
  end
end