Add solution for Day 17 puzzle

Author: akdemironur

17/sample_input

@@ -0,0 +1,13 @@
+2413432311323
+3215453535623
+3255245654254
+3446585845452
+4546657867536
+1438598798454
+4457876987766
+3637877979653
+4654967986887
+4564679986453
+1224686865563
+2546548887735
+4322674655533

17/sol.exs

@@ -0,0 +1,105 @@
+defmodule Day17 do
+  def read_input(file_path) do
+    File.read!(file_path)
+    |> String.split("\n", trim: true)
+    |> Enum.map(fn line -> String.graphemes(line) |> Enum.map(&String.to_integer/1) end)
+  end
+
+  def get_heat({x, y}, heatmap) do
+    case heatmap |> Enum.at(x) do
+      nil -> nil
+      line -> Enum.at(line, y)
+    end
+  end
+
+  def apply_dir_to_pos({x, y}, {dx, dy}), do: {x + dx, y + dy}
+  @dirs [{1, 0}, {0, -1}, {-1, 0}, {0, 1}]
+
+  def next_states(heatmap, {gridX, gridY}, costs, min_dist, max_dist, [
+        {{{x, y}, _, dist}, _} | rest
+      ])
+      when x < 0 or y < 0 or gridX <= x or gridY <= y or dist > max_dist,
+      do: next_states(heatmap, {gridX, gridY}, costs, min_dist, max_dist, rest)
+
+  def next_states(heatmap, grid_lims, costs, min_dist, max_dist, [
+        {{pos, dir, dist}, current_cost} | rest
+      ]) do
+    new_current_cost = get_heat(pos, heatmap) + current_cost
+
+    if !(costs |> Map.get({pos, dir, dist}) <= new_current_cost) do
+      new_costs = Map.put(costs, {pos, dir, dist}, new_current_cost)
+
+      new_pos_dir_dists =
+        if dist < min_dist do
+          [
+            {{apply_dir_to_pos(pos, Enum.at(@dirs, dir)), dir, dist + 1}, new_current_cost}
+            | rest
+          ]
+        else
+          [
+            {{apply_dir_to_pos(pos, Enum.at(@dirs, dir)), dir, dist + 1}, new_current_cost}
+            | [
+                {{apply_dir_to_pos(pos, Enum.at(@dirs, Integer.mod(dir + 1, 4))),
+                  Integer.mod(dir + 1, 4), 1}, new_current_cost}
+                | [
+                    {{apply_dir_to_pos(pos, Enum.at(@dirs, Integer.mod(dir + 3, 4))),
+                      Integer.mod(dir + 3, 4), 1}, new_current_cost}
+                    | rest
+                  ]
+              ]
+          ]
+        end
+
+      next_states(
+        heatmap,
+        grid_lims,
+        new_costs,
+        min_dist,
+        max_dist,
+        new_pos_dir_dists
+      )
+    else
+      next_states(heatmap, grid_lims, costs, min_dist, max_dist, rest)
+    end
+  end
+
+  def next_states(_, _, costs, _, _, []), do: costs
+
+  def next_states(heatmap, min_dist, max_dist),
+    do:
+      next_states(
+        heatmap,
+        {length(heatmap), length(Enum.at(heatmap, 0))},
+        %{},
+        min_dist,
+        max_dist,
+        [{{{0, 1}, 3, 1}, 0}]
+      )
+
+  def solve(hm, min_dist, max_dist) do
+    hm
+    |> next_states(min_dist, max_dist)
+    |> Map.to_list()
+    |> Enum.map(fn {{{x, y}, _, dist}, cost} -> {{x, y, dist}, cost} end)
+    |> Enum.filter(fn {{x, y, dist}, _} ->
+      dist >= min_dist and x == length(hm) - 1 and y == length(Enum.at(hm, 0)) - 1
+    end)
+    |> Enum.map(fn {{_, _, _}, cost} -> cost end)
+    |> Enum.min()
+  end
+
+  def partA(file_path) do
+    file_path
+    |> read_input()
+    |> solve(1, 3)
+  end
+
+  def partB(file_path) do
+    file_path
+    |> read_input()
+    |> solve(4, 10)
+  end
+end
+
+IO.puts(Day17.partA("./input"))
+IO.puts(Day17.partB("./input"))