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# Day 15
```elixir
Mix.install([
{:kino, "~> 0.14.2"},
{:kino_aoc, "~> 0.1.7"}
])
```
## Part 1
```elixir
example = """
##########
#..O..O.O#
#......O.#
#.OO..O.O#
#..O@..O.#
#O#..O...#
#O..O..O.#
#.OO.O.OO#
#....O...#
##########
<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^
"""
{:ok, input} = if true do
KinoAOC.download_puzzle("2024", "15", System.fetch_env!("LB_AOC_SESSION"))
else
{:ok, example}
end
[grid, moves] = input
|> String.trim()
|> String.split("\n\n")
|> Enum.map(&String.trim/1)
moves = String.graphemes(moves) |> Enum.filter(& &1 != "\n")
grid = grid |> String.split("\n") |> Enum.map(&String.graphemes/1)
{size_r, size_c} = { # Used for printing
length(grid) - 1,
length(Enum.at(grid, 0)) - 1
}
grid = for {row, i} <- Enum.with_index(grid) do
for {col, j} <- Enum.with_index(row) do
{{i, j}, col}
end
end |> List.flatten()
bot_start = List.keyfind(grid, "@", 1)
grid = Enum.into(grid, %{})
```
```elixir
# Make a pretty picture
print_grid = fn grid ->
for r <- 0..size_r do
row = for c <- 0..size_c do
Map.get(grid, {r, c})
end
IO.puts(List.to_string(row))
end
end
defmodule Part1 do
# Get coordinate and value of cell in given direction
def get_next(dir, {ri, ci}, grid) do
pos = case dir do
">" -> {ri, ci + 1}
"<" -> {ri, ci - 1}
"v" -> {ri + 1, ci}
"^" -> {ri - 1, ci}
end
val = Map.get(grid, pos)
{pos, val}
end
# Handles lists of directions
def move(grid, _, []), do: grid
def move(grid, pos_val, [dir | rest]) do
{pv1, grid} = move(grid, pos_val, dir)
move(grid, pv1, rest)
end
# Returns position, value, and grid (with no change for invalid moves)
def move(grid, this = {pos, val}, dir) do
{pos1, val1} = get_next(dir, pos, grid)
case val1 do
"#" -> {this, grid}
"." -> grid = Map.replace(grid, pos1, val) |> Map.replace(pos, ".")
{{pos1, val}, grid}
"O" -> {pv2, grid} = move(grid, {pos1, val1}, dir)
if pv2 != {pos1, val1}, do: grid |> move(this, dir), else: {this, grid}
end
end
end
grid = Part1.move(grid, bot_start, moves)
print_grid.(grid)
```
```elixir
result = Map.to_list(grid)
|> Enum.filter(fn {_, v} -> v == "O" end) # Filter to boxes
|> Enum.map(fn {{r, c}, _} -> 100 * r + c end) # Calculate coordinates
|> Enum.sum()
```
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