Add Elixir example for longest common subsequence

09_dynamic_programming/elixir/01_longest_common_subsequence.exs

@@ -0,0 +1,12 @@
+# `cell` is a map of maps here, e.g.
+# cell = %{
+#   0 => %{0 => 0, ...},
+#   1 => %{...},
+#   ...
+# }
+
+if String.at(word_a, i) == String.at(word_a, j) do
+  put_in(cell[i - 1][j - 1], cell[i - 1][j - 1] + 1)
+else
+  put_in(cell[i - 1][j - 1], max(cell[i - 1][j], cell[i][j - 1]))
+end