Week 4 solutions

Author: han

counting-bits/han.exs

@@ -0,0 +1,8 @@
+defmodule Solution do
+  @spec count_bits(n :: integer) :: [integer]
+  def count_bits(n) do
+    Enum.map(0..n, fn i ->
+      Integer.digits(i, 2) |> Enum.count(&(&1 != 0))
+    end)
+  end
+end

group-anagrams/han.exs

@@ -0,0 +1,31 @@
+defmodule Solution do
+  @spec group_anagrams(strs :: [String.t]) :: [[String.t]]
+  def group_anagrams(strs) do
+    Enum.group_by(strs, &(String.codepoints(&1) |> Enum.sort)) |> Map.values
+  end
+end
+
+# 최초엔 아래 코드로 시도했으나 strs.length가 커지면 시간초과...
+#
+# defmodule Solution do
+#   @spec group_anagrams(strs :: [String.t]) :: [[String.t]]
+#   def group_anagrams(strs) when length(strs) < 2, do: [strs]
+#   def group_anagrams([], res), do: res
+
+#   def group_anagrams([head|tail], res \\ []) do
+#     split_sort_head = split_sort(head)
+#     anagrams = Enum.reduce(tail, [head], fn x, acc ->
+#       if split_sort(x) == split_sort_head do
+#         acc ++ [x]
+#       else
+#         acc
+#       end
+#     end)
+
+#     group_anagrams(tail -- anagrams, [anagrams|res])
+#   end
+
+#   defp split_sort(str) do
+#     String.graphemes(str) |> Enum.sort_by(&(&1), :asc)
+#   end
+# end

missing-number/han.exs

@@ -0,0 +1,6 @@
+defmodule Solution do
+  @spec missing_number(nums :: [integer]) :: integer
+  def missing_number(nums) do
+    (0..length(nums) |> Enum.to_list) -- nums |> Enum.at(0)
+  end
+end

number-of-1-bits/han.exs

@@ -0,0 +1,6 @@
+defmodule Solution do
+  @spec hamming_weight(n :: integer) :: integer
+  def hamming_weight(n) do
+    Integer.to_string(n, 2) |> String.graphemes |> Enum.count(& &1 != "0")
+  end
+end

reverse-bits/han.rb

@@ -0,0 +1,6 @@
+# @param {Integer} n, a positive integer
+# @return {Integer}
+def reverse_bits(n)
+    # 이유는 모르겠으나 문제 설명과는 달리 leetcode 루비 테스트코드에선 n이 10진수 Integer로 들어오네요.
+    n.to_s(2).rjust(32,'0').reverse.to_i(2)
+end