From 5b7a124ecbfdfd8376bcfa12028fef7b08abc58d Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Tue, 8 Dec 2020 09:14:26 -0500
Subject: [PATCH] Day 8

---
 lib/day8/day8.ex   |  82 ++++++
 lib/day8/input.txt | 631 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 713 insertions(+)
 create mode 100644 lib/day8/day8.ex
 create mode 100644 lib/day8/input.txt

diff --git a/lib/day8/day8.ex b/lib/day8/day8.ex
new file mode 100644
index 0000000..21b9db8
--- /dev/null
+++ b/lib/day8/day8.ex
@@ -0,0 +1,82 @@
+defmodule Day8 do
+  @example """
+  nop +0
+  acc +1
+  jmp +4
+  acc +3
+  jmp -3
+  acc -99
+  acc +1
+  jmp -4
+  acc +6
+  """
+
+  def part1(example \\ false) do
+    if(example, do: @example, else: File.read!("lib/day8/input.txt"))
+    |> parse_prog()
+    |> run_stopping_after_repetition()
+  end
+
+  def part2(example \\ false) do
+    prog =
+      if(example, do: @example, else: File.read!("lib/day8/input.txt"))
+      |> parse_prog()
+
+    prog
+    |> Enum.with_index()
+    |> Enum.filter(fn
+      {{"acc", _}, _} -> false
+      _ -> true
+    end)
+    |> Enum.find_value(fn {{insn, val}, index} ->
+      new_insn = if insn == "nop", do: "jmp", else: "nop"
+      modified_prog = List.replace_at(prog, index, {new_insn, val})
+
+      case run_stopping_after_repetition(modified_prog) do
+        {:loop, _} -> false
+        {:halt, acc} -> acc
+      end
+    end)
+  end
+
+  def parse_prog(str) do
+    str
+    |> String.trim()
+    |> String.split("\n")
+    |> Enum.map(&parse_insn/1)
+  end
+
+  def parse_insn(str) do
+    [_, insn, num] = Regex.run(~r/^(\w+) ([+-]\d+)$/, str)
+    num = String.to_integer(num)
+    {insn, num}
+  end
+
+  def run_stopping_after_repetition(prog, {acc, ip, visited_insns} \\ {0, 0, MapSet.new()}) do
+    cond do
+      MapSet.member?(visited_insns, ip) ->
+        {:loop, acc}
+
+      ip >= length(prog) ->
+        {:halt, acc}
+
+      true ->
+        insn = Enum.at(prog, ip)
+        old_ip = ip
+        {acc, ip} = run_insn(insn, acc, ip)
+        run_stopping_after_repetition(prog, {acc, ip, MapSet.put(visited_insns, old_ip)})
+    end
+  end
+
+  def run_insn({"nop", _}, acc, ip) do
+    {acc, ip + 1}
+  end
+
+  def run_insn({"acc", val}, acc, ip) do
+    {acc + val, ip + 1}
+  end
+
+  def run_insn({"jmp", val}, acc, ip) do
+    {acc, ip + val}
+  end
+end
diff --git a/lib/day8/input.txt b/lib/day8/input.txt
new file mode 100644
index 0000000..bdc7017
--- /dev/null
+++ b/lib/day8/input.txt
@@ -0,0 +1,631 @@
+nop +355
+acc +46
+jmp +42
+jmp +585
+acc +11
+acc +0
+acc +40
+jmp +284
+acc -2
+nop +276
+jmp +613
+acc +23
+acc +2
+acc +14
+acc +25
+jmp +310
+acc +43
+acc +43
+jmp +510
+jmp +116
+jmp +204
+nop +213
+acc +47
+jmp +1
+acc +8
+jmp +461
+jmp -22
+acc +36
+acc +33
+acc +45
+jmp +175
+acc +21
+jmp +472
+acc +50
+acc +40
+jmp +525
+acc +26
+nop +208
+jmp +496
+jmp +153
+acc +50
+acc +24
+nop +512
+jmp +242
+acc +7
+nop +317
+acc +50
+acc +7
+jmp +268
+acc +8
+acc -19
+acc -11
+jmp +1
+jmp +383
+acc +1
+jmp +230
+acc +5
+jmp +128
+nop +227
+acc -7
+jmp -16
+acc +11
+acc -6
+jmp -42
+acc +11
+acc +23
+jmp +7
+jmp -23
+jmp +11
+acc +0
+nop +246
+acc +24
+jmp +213
+jmp +550
+acc +24
+acc +14
+acc +34
+acc -6
+jmp +525
+acc +4
+nop +220
+jmp +399
+acc +41
+jmp +34
+acc -2
+acc +38
+acc +48
+acc -7
+jmp +136
+acc -2
+acc +40
+acc +12
+acc -4
+jmp +467
+acc +36
+acc +19
+nop +518
+jmp +328
+acc +7
+nop +263
+acc +19
+acc -17
+jmp +282
+jmp +206
+acc +28
+acc +7
+jmp +417
+acc -10
+jmp -75
+nop +475
+nop +68
+nop -38
+acc +33
+jmp +367
+acc +0
+jmp +459
+jmp +1
+acc +50
+jmp +1
+nop -25
+jmp +464
+acc +35
+jmp -5
+acc -14
+jmp -113
+nop +25
+acc +33
+acc +28
+acc +3
+jmp -71
+nop +75
+acc +19
+acc +27
+jmp +332
+jmp +361
+acc -2
+acc +45
+acc +47
+jmp +461
+jmp -120
+acc +18
+acc +25
+acc +11
+jmp +24
+jmp +372
+acc +32
+acc +2
+jmp +87
+acc +23
+jmp +96
+acc +32
+nop +233
+acc -7
+jmp +435
+jmp +51
+acc -7
+jmp +392
+acc +22
+acc -17
+acc +8
+acc +34
+jmp -140
+acc +10
+nop +276
+jmp -57
+acc -6
+jmp +388
+acc +4
+jmp +386
+jmp +267
+jmp +1
+acc +15
+acc -11
+nop -169
+jmp +71
+acc +10
+acc +19
+jmp +377
+acc -1
+jmp +316
+acc +13
+acc -5
+acc +7
+acc +28
+jmp -49
+acc +20
+acc +4
+acc -19
+jmp +196
+acc -1
+acc -8
+jmp +266
+acc +43
+acc +10
+nop +122
+jmp +222
+acc +0
+jmp +275
+nop +282
+jmp +199
+acc +24
+acc +37
+acc -18
+nop -33
+jmp -110
+acc -7
+acc -9
+acc +18
+jmp -189
+acc -10
+acc +46
+jmp +214
+acc +22
+acc +45
+jmp +48
+nop +217
+acc -6
+acc +5
+jmp -40
+jmp +220
+acc +26
+nop +393
+jmp +1
+jmp +358
+jmp +138
+nop -181
+acc +48
+jmp +190
+acc +49
+jmp +105
+jmp -176
+jmp +37
+acc +49
+jmp -130
+acc +20
+acc +48
+jmp +236
+acc +41
+acc +19
+nop +321
+jmp -12
+acc +3
+acc +38
+jmp +338
+jmp -160
+nop +250
+acc +21
+jmp +29
+acc +44
+acc +11
+acc -17
+acc +7
+jmp +110
+nop +242
+acc +48
+acc +46
+jmp -15
+acc -18
+nop -190
+acc +39
+acc -12
+jmp +255
+acc -16
+acc -13
+acc +12
+acc +29
+jmp +243
+jmp -14
+acc +33
+nop +40
+acc -11
+jmp +252
+nop +248
+acc -17
+acc +14
+jmp +29
+acc -6
+acc +21
+acc +27
+nop +287
+jmp +329
+acc -3
+acc +7
+acc +0
+jmp +297
+acc +9
+jmp -10
+acc +11
+nop +293
+acc -14
+jmp +214
+acc -11
+acc +43
+acc +43
+acc +35
+jmp +239
+acc +10
+acc -18
+acc +39
+jmp -129
+acc +8
+jmp +313
+acc +49
+jmp +300
+nop +219
+nop +215
+jmp -203
+acc -8
+jmp +137
+nop +211
+acc -19
+acc -18
+nop -8
+jmp +132
+acc -17
+jmp -84
+acc +8
+acc +2
+acc -1
+jmp -91
+acc -4
+acc +37
+jmp +1
+acc +14
+jmp -297
+acc -10
+nop -186
+acc -18
+jmp -150
+acc +46
+acc +25
+acc +45
+acc -5
+jmp +187
+acc +21
+jmp +101
+acc +15
+acc -15
+jmp +30
+acc +42
+acc +35
+jmp +276
+jmp -323
+jmp -124
+acc +34
+acc -16
+acc -19
+jmp -314
+acc +45
+jmp -219
+acc +6
+acc -12
+acc +45
+acc +38
+jmp +30
+acc +32
+acc +47
+acc +40
+acc +11
+jmp -236
+acc +46
+jmp -328
+acc -18
+acc +34
+acc -11
+jmp +201
+acc +8
+jmp +161
+nop +44
+acc +8
+jmp +158
+acc +26
+jmp +137
+acc +2
+acc -4
+nop -59
+jmp +14
+acc +18
+jmp -211
+acc +28
+jmp -152
+acc -3
+acc +0
+jmp -21
+acc -2
+jmp -331
+acc +1
+acc +24
+nop -274
+jmp -350
+jmp +1
+acc +28
+acc -14
+acc +49
+jmp -39
+nop +114
+acc +33
+jmp +217
+acc +0
+acc +25
+jmp +1
+acc +33
+jmp +50
+acc +23
+acc +0
+acc -14
+jmp +66
+jmp -68
+jmp +1
+acc +0
+acc +10
+jmp -244
+jmp -200
+jmp +1
+acc -2
+acc +34
+jmp -48
+nop +192
+acc +34
+acc -1
+acc +6
+jmp -48
+acc +4
+acc +13
+jmp -405
+acc +36
+nop -372
+acc +20
+acc +32
+jmp -231
+acc +14
+jmp -83
+acc +22
+jmp -375
+acc +21
+jmp -356
+acc -1
+jmp -398
+jmp -104
+acc +48
+nop -382
+jmp -296
+acc -15
+acc +29
+jmp +159
+acc +41
+jmp -215
+acc -6
+acc -1
+acc +44
+acc -14
+jmp +72
+acc +2
+acc +6
+jmp -106
+acc +39
+jmp -301
+acc -12
+acc +43
+acc +24
+jmp -53
+nop +19
+acc +17
+acc -12
+jmp -211
+jmp +1
+jmp -98
+acc +18
+acc -6
+nop -153
+nop -376
+jmp -377
+nop +109
+acc -10
+acc +6
+acc -13
+jmp -359
+acc +35
+nop +125
+jmp -312
+jmp -23
+acc +8
+acc +27
+nop +105
+acc -16
+jmp -112
+acc -9
+acc +13
+acc +1
+jmp -421
+nop -471
+acc +41
+acc +10
+acc +26
+jmp -110
+acc -8
+acc -17
+acc +32
+acc -3
+jmp -329
+acc +0
+acc +2
+acc +2
+jmp +114
+acc +44
+acc +7
+acc -8
+jmp +33
+jmp -310
+nop -14
+acc +32
+acc +21
+acc +42
+jmp -509
+acc +4
+jmp -29
+nop +12
+nop +74
+jmp -491
+jmp -307
+acc +12
+jmp -217
+jmp -254
+nop -3
+acc +33
+jmp +101
+acc +17
+jmp -4
+nop -361
+acc +20
+acc +0
+acc +37
+jmp -120
+jmp -178
+jmp -306
+acc +31
+acc +16
+acc +12
+nop +61
+jmp -466
+acc +38
+acc +40
+jmp -323
+acc -1
+nop -112
+nop +46
+nop -221
+jmp -111
+jmp -248
+acc -2
+nop +53
+acc -12
+nop -382
+jmp -514
+jmp +1
+acc +30
+jmp -177
+acc -18
+acc +34
+jmp -297
+jmp -446
+nop -33
+acc +8
+acc +19
+acc +22
+jmp +16
+acc -17
+nop -194
+jmp -541
+acc +50
+acc +15
+nop -347
+acc -9
+jmp -433
+acc +32
+nop -571
+jmp -482
+acc +42
+nop -287
+nop -263
+jmp -368
+jmp +10
+acc +39
+jmp -204
+acc +28
+acc +35
+jmp -565
+jmp -464
+jmp -84
+acc +25
+jmp -532
+acc +42
+jmp +1
+jmp -154
+acc +4
+acc +8
+acc +4
+acc +48
+jmp -82
+jmp -256
+acc +33
+acc +49
+jmp +1
+jmp -539
+acc -1
+acc +46
+acc +49
+acc +13
+jmp -20
+acc -11
+acc -15
+acc +1
+jmp -96
+jmp -483
+jmp -444
+jmp +1
+jmp -382
+acc -5
+acc +5
+acc +26
+jmp -458
+acc +24
+jmp -515
+nop -211
+jmp -64
+jmp -246
+acc -17
+acc -7
+acc +0
+acc +21
+jmp +1