top_k_frequent, 3sum

Author: h

3sum/han.exs

@@ -0,0 +1,38 @@
+defmodule Solution do
+  @spec three_sum(nums :: [integer]) :: [[integer]]
+  def three_sum(nums) do
+    length_of_nums = length nums
+    num_index_map = nums |> Enum.with_index |> Map.new
+    frequencies_of_num = nums |> Enum.frequencies()
+    tuple_nums = nums |> List.to_tuple
+    num_indexs_map = nums |>
+      Enum.with_index() |>
+      Enum.group_by(fn {v, _} -> v end, fn {_, i} -> i end)
+
+    Stream.unfold({0, 1}, fn {i, j} ->
+      if j < length_of_nums - 1,
+      do: {{i, j}, {i, j + 1}},
+      else: {{i, j}, {i + 1, i + 2}}
+    end) |>
+      Stream.take_while(fn {i, _} ->
+        i < length_of_nums - 1
+      end) |>
+      Stream.map(fn {i, j} ->
+        a = elem tuple_nums, i
+        b = elem tuple_nums, j
+        c = -(a + b)
+
+        case frequencies_of_num[c] do
+          nil -> nil
+          count when count >= 3 -> [a, b, c] |> Enum.sort()
+          _ ->
+            if num_indexs_map[c] |> Enum.filter(& &1 != i && &1 != j) |> Enum.at(0),
+            do: [a, b, c] |> Enum.sort(),
+            else: nil
+        end
+      end) |>
+      Stream.reject(& &1 == nil) |>
+      Stream.uniq |>
+      Enum.to_list
+  end
+end

top-k-frequent-elements/han.exs

@@ -0,0 +1,10 @@
+defmodule Solution do
+  @spec top_k_frequent(nums :: [integer], k :: integer) :: [integer]
+  def top_k_frequent(nums, k) do
+    nums |>
+      Enum.frequencies |>
+      Enum.sort_by(fn {_, v} -> v end, :desc) |>
+      Enum.take(k) |>
+      Enum.map(fn {k, _} -> k end)
+  end
+end