Week 1 solutions - 김한기

best-time-to-buy-and-sell-stock/han.exs

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+defmodule Solution do
+  @spec max_profit(prices :: [integer]) :: integer
+  def max_profit([head | tail]) do
+        {_, answer} = Enum.reduce(tail, {head, 0}, fn x, {buy, profit} ->
+            {min(buy, x), max(profit, x - buy)}
+        end)
+
+        answer
+    end
+end

contains-duplicate/han.exs

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+defmodule Solution do
+  @spec contains_duplicate(nums :: [integer]) :: boolean
+  def contains_duplicate(nums) do
+    if nums |> Enum.into(MapSet.new) |> Enum.to_list |> length == length(nums) do
+        false
+    else
+        true
+    end
+  end
+end

two-sum/han.exs

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+defmodule Solution do
+    def two_sum([head | tail], target, index\\0) do
+        second_index = Enum.find_index(tail, fn element -> 
+            head + element == target
+        end)
+
+        if second_index, do: [index, second_index + index + 1], else: two_sum(tail, target, index + 1)
+    end
+end

valid-anagram/han.exs

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+defmodule Solution do
+  @spec is_anagram(s :: String.t, t :: String.t) :: boolean
+  def is_anagram(s, t) do
+    s |> String.split("", trim: true) |> Enum.sort == t |> String.split("", trim: true) |> Enum.sort
+  end
+end

valid-palindrome/han.exs

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+defmodule Solution do
+  @spec is_palindrome(s :: String.t) :: boolean
+  def is_palindrome(s) do
+    non_alphanumeric_ascii_codes = [?a..?z, ?0..?9] |>
+        Enum.reduce([], fn x, acc -> 
+            acc ++ (x |> Enum.to_list)
+        end)
+    converted = s
+        |> String.downcase
+        |> String.replace(~r/./, fn char ->
+            if :binary.first(char) in non_alphanumeric_ascii_codes, do: char, else: ""
+        end)
+
+    length = converted |> String.length
+
+    if length < 2, do: true
+
+    center = length |> div(2)
+
+    converted |> String.slice(0..center) ==
+        converted
+        |> String.slice(-(center+1)..-1)
+        |> String.reverse
+  end
+end