From 690f55f0ad0451589dbb4bae4499778d6f9a20f0 Mon Sep 17 00:00:00 2001
From: Colin McMillen <colin@semicolin.games>
Date: Tue, 8 Dec 2020 15:23:20 -0500
Subject: [PATCH] day 8 solution

---
 2020/Day08.cs  | 122 +++++++++
 2020/day08.txt | 651 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 773 insertions(+)
 create mode 100644 2020/Day08.cs
 create mode 100644 2020/day08.txt

diff --git a/2020/Day08.cs b/2020/Day08.cs
new file mode 100644
index 0000000..4186181
--- /dev/null
+++ b/2020/Day08.cs
@@ -0,0 +1,122 @@
+using System;
+using static System.Console;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+using Xunit;
+
+namespace AdventOfCode {
+
+  public class Day08 {
+
+    public class GameConsole {
+      int accumulator = 0;
+      int pointer = 0;
+
+      // Returns a (bool, int) tuple, where the bool indicates whether the program terminated
+      // normally (if false, it executed an infinite loop), and the int indicates the value of
+      // the accumulator at the time of termination.
+      public (bool, int) Execute(List<Instruction> code) {
+        var instructionsExecuted = new HashSet<int>();
+        while (pointer < code.Count()) {
+          if (instructionsExecuted.Contains(pointer)) {
+            return (false, accumulator);  // loop detected
+          }
+          instructionsExecuted.Add(pointer);
+          Instruction instruction = code[pointer];
+          switch (instruction.Op) {
+            case "nop":
+              pointer++;
+              break;
+            case "acc":
+              pointer++;
+              accumulator += instruction.Value;
+              break;
+            case "jmp":
+              pointer += instruction.Value;
+              break;
+            default:
+              throw new Exception("invalid op");
+          }
+        }
+        return (true, accumulator);  // normal termination
+      }
+    }
+
+    public record Instruction(string Op, int Value);
+
+    public static int RepairBrokenInstruction(List<Instruction> code) {
+      for (int i = 0; i < code.Count(); i++) {
+        if (code[i].Op == "acc") {
+          continue;  // this line can't be the broken one
+        }
+        List<Instruction> repaired = new List<Instruction>(code);
+        if (repaired[i].Op == "nop") {
+          repaired[i] = new Instruction("jmp", repaired[i].Value);
+        } else {
+          repaired[i] = new Instruction("nop", repaired[i].Value);
+        }
+        var (success, result) = new GameConsole().Execute(repaired);
+        if (success) {
+          return result;
+        }
+      }
+      throw new Exception("didn't find a valid instruction to repair");
+    }
+
+    static List<Instruction> ParseInstructions(string[] code) {
+      var result = new List<Instruction>();
+      foreach (string line in code) {
+        string[] tokens = line.Split(' ');
+        result.Add(new Instruction(tokens[0], int.Parse(tokens[1])));
+      }
+      return result;
+    }
+
+    static int Part1() {
+      string[] input = File.ReadAllLines(Util.RootDir + "day08.txt");
+      List<Instruction> code = ParseInstructions(input);
+      (bool finished, int result) = new GameConsole().Execute(code);
+      return result;
+    }
+
+    static int Part2() {
+      string[] input = File.ReadAllLines(Util.RootDir + "day08.txt");
+      List<Instruction> code = ParseInstructions(input);
+      return RepairBrokenInstruction(code);
+    }
+
+    [Fact]
+    public static void Test() {
+      string[] example =
+@"nop +0
+acc +1
+jmp +4
+acc +3
+jmp -3
+acc -99
+acc +1
+jmp -4
+acc +6".Split('\n');
+      List<Instruction> parsed = ParseInstructions(example);
+      Assert.Equal(9, parsed.Count());
+      Assert.Equal((false, 5), new GameConsole().Execute(parsed));
+      Assert.Equal(1610, Part1());
+
+      string[] example2 =
+@"nop +0
+acc +1
+jmp +4
+acc +3
+jmp -3
+acc -99
+acc +1
+nop -4
+acc +6".Split('\n');
+      List<Instruction> parsed2 = ParseInstructions(example2);
+      Assert.Equal((true, 8), new GameConsole().Execute(parsed2));
+      Assert.Equal(1703, Part2());
+    }
+  }
+}
diff --git a/2020/day08.txt b/2020/day08.txt
new file mode 100644
index 0000000..7b4ebab
--- /dev/null
+++ b/2020/day08.txt
@@ -0,0 +1,651 @@
+jmp +1
+acc -18
+acc +19
+acc +19
+jmp +202
+acc +15
+acc +42
+acc +30
+acc -7
+jmp +535
+acc +31
+acc +9
+jmp +581
+nop +501
+acc +44
+acc +18
+acc -4
+jmp +545
+acc +9
+acc +5
+nop -2
+acc +3
+jmp +475
+acc -10
+acc +14
+acc +29
+nop +471
+jmp +470
+acc +2
+nop +375
+acc +31
+acc +6
+jmp +420
+acc -1
+acc +2
+nop +185
+jmp +490
+acc +2
+jmp +317
+nop +282
+jmp +457
+acc +37
+jmp +254
+acc +19
+jmp +436
+jmp +458
+acc -7
+acc -2
+acc -17
+jmp +454
+acc +37
+jmp +212
+acc +6
+acc +5
+acc -7
+jmp +104
+acc +5
+nop +134
+acc +46
+jmp +541
+acc +4
+acc +46
+acc +18
+jmp -53
+acc +10
+jmp +285
+acc +39
+acc +34
+nop +109
+acc +47
+jmp +32
+jmp +1
+jmp +143
+acc +36
+jmp +429
+acc +45
+acc +22
+jmp -59
+acc +0
+acc +23
+acc +30
+acc -7
+jmp -45
+acc +46
+acc +31
+jmp +164
+acc +37
+acc +34
+acc +40
+acc -1
+jmp +246
+nop -46
+acc +2
+acc +31
+jmp +221
+nop +413
+jmp -51
+acc -14
+jmp +145
+acc +1
+nop +77
+jmp +131
+jmp +370
+nop +513
+acc +7
+jmp +476
+acc +22
+acc +37
+acc +44
+jmp +334
+acc +9
+acc -1
+acc +5
+acc +27
+jmp +351
+acc +31
+jmp +220
+nop -61
+acc +34
+jmp +504
+nop +471
+acc +6
+acc +48
+jmp -17
+jmp +217
+acc +13
+acc +0
+acc +25
+jmp +144
+acc -5
+acc +17
+nop +341
+jmp -26
+acc -10
+acc +34
+jmp +168
+nop -16
+acc -6
+acc -10
+acc +38
+jmp +30
+acc -2
+acc -14
+jmp +419
+acc +40
+acc -17
+acc +27
+acc +8
+jmp +101
+nop +370
+acc +2
+acc -10
+acc -7
+jmp +224
+nop +437
+acc +42
+acc +50
+acc +39
+jmp +81
+jmp +11
+jmp +143
+acc +6
+acc +46
+jmp -107
+acc +13
+jmp -109
+acc +5
+jmp +1
+jmp +467
+jmp -159
+nop +421
+jmp +243
+acc +44
+nop +412
+acc -6
+acc +13
+jmp +56
+acc -12
+acc +18
+jmp +313
+nop +151
+acc +5
+acc +49
+jmp +120
+acc +46
+acc +23
+nop -122
+acc +21
+jmp -55
+acc -15
+jmp -115
+acc +19
+nop +116
+acc +32
+acc +21
+jmp +16
+acc +27
+acc +32
+jmp +359
+acc +16
+acc +18
+acc +15
+jmp +54
+nop +182
+acc +4
+jmp +361
+acc +4
+acc +38
+acc +49
+jmp -94
+jmp +428
+acc +0
+acc +9
+jmp +224
+jmp +82
+nop +57
+acc +6
+jmp +1
+jmp +144
+jmp +20
+jmp +265
+jmp +402
+nop +114
+acc -12
+acc -11
+acc +1
+jmp +412
+nop -163
+acc +50
+acc +1
+acc -9
+jmp -20
+acc +10
+acc +6
+jmp +323
+acc +10
+jmp +1
+acc +42
+jmp +46
+acc +35
+acc +31
+jmp -139
+jmp +129
+jmp -193
+acc -4
+nop +247
+nop -163
+acc +25
+jmp -26
+acc +34
+acc +26
+acc +40
+jmp +220
+acc -6
+acc +6
+jmp +311
+acc +0
+acc +14
+acc +41
+acc +6
+jmp +284
+acc +32
+jmp -13
+nop +157
+acc -4
+acc +47
+jmp -146
+acc +34
+acc +6
+nop +196
+acc +5
+jmp +268
+acc -8
+jmp -176
+acc +34
+acc +17
+jmp +1
+jmp +114
+acc +32
+acc +39
+nop +313
+acc +38
+jmp -237
+jmp -273
+acc +21
+acc +26
+acc +31
+jmp -231
+acc +17
+jmp -105
+nop +333
+nop +17
+jmp +11
+acc -9
+acc +2
+jmp -162
+acc +3
+acc +0
+nop +318
+jmp +215
+acc +14
+acc +32
+jmp -196
+jmp +33
+acc -6
+acc +45
+acc +27
+jmp -166
+acc -1
+jmp -25
+acc +0
+acc +4
+acc -14
+acc +0
+jmp -115
+nop +118
+acc +28
+nop +175
+acc +45
+jmp -97
+jmp +78
+jmp -284
+acc +35
+nop -248
+acc -18
+acc -6
+jmp -308
+jmp -95
+acc -2
+acc +0
+jmp +255
+acc +7
+jmp -24
+acc +17
+acc +20
+jmp -220
+jmp +172
+acc +40
+acc +39
+acc +19
+jmp -238
+nop +44
+nop -99
+nop +238
+jmp +195
+acc -14
+acc +36
+acc +40
+acc -11
+jmp -65
+nop -54
+nop +47
+acc -11
+jmp +18
+jmp +98
+jmp +252
+nop -1
+acc +1
+acc +10
+jmp -4
+jmp -319
+jmp -46
+acc -8
+acc +50
+acc +43
+jmp -174
+acc +22
+acc +4
+acc +32
+acc -6
+jmp +73
+acc +8
+jmp -31
+acc +16
+nop +11
+acc +26
+jmp -98
+acc -11
+acc +40
+jmp +101
+acc +28
+acc +30
+acc -16
+acc +7
+jmp +239
+jmp -179
+acc +47
+acc +15
+acc +42
+acc +26
+jmp +30
+acc +17
+acc +3
+acc -5
+nop -98
+jmp -236
+acc +2
+jmp +196
+acc +39
+acc -14
+acc +36
+acc +49
+jmp +189
+jmp +235
+acc +27
+acc -2
+acc +16
+acc +40
+jmp -81
+acc -5
+acc +17
+acc -1
+jmp +1
+jmp -129
+nop -171
+acc +47
+jmp +169
+acc -16
+acc -5
+jmp +172
+nop -84
+acc +8
+acc +40
+acc +43
+jmp -33
+acc +39
+nop -12
+jmp +53
+acc +36
+jmp -270
+acc +17
+acc -1
+jmp -255
+acc +0
+acc -12
+jmp -371
+jmp -216
+acc +45
+acc -18
+acc +23
+acc -17
+jmp -37
+jmp -386
+nop -302
+acc -19
+acc -16
+jmp -297
+acc -18
+acc -7
+acc +17
+acc +17
+jmp -173
+jmp +114
+acc +4
+acc +19
+nop -296
+jmp -36
+acc -18
+acc -14
+acc +6
+nop -27
+jmp -101
+acc +15
+nop -407
+jmp +44
+acc -18
+acc -6
+acc +33
+acc +36
+jmp +80
+acc +43
+jmp +73
+acc -2
+acc +7
+acc +4
+jmp -10
+acc +46
+nop -49
+acc +7
+jmp +65
+acc +24
+jmp +144
+acc +13
+acc +26
+jmp -351
+jmp +1
+acc +34
+nop +62
+jmp -363
+acc -4
+acc -5
+jmp +23
+jmp +82
+acc -7
+acc -7
+acc +15
+jmp -468
+acc +7
+nop -423
+jmp -178
+nop -425
+acc +23
+jmp -181
+acc +6
+acc -11
+jmp -321
+acc +3
+jmp -122
+acc +12
+jmp +44
+acc -5
+acc -16
+acc +16
+jmp -281
+acc +33
+acc -4
+acc +15
+jmp +9
+jmp +63
+acc +35
+nop -12
+acc +25
+acc -10
+jmp -452
+acc +1
+jmp -148
+acc +8
+acc +40
+acc +48
+jmp +2
+jmp -315
+nop -325
+acc -4
+acc +16
+acc -4
+jmp -369
+acc +21
+acc +3
+jmp -153
+nop -25
+acc +0
+jmp -84
+acc +32
+jmp +19
+acc -18
+acc -1
+jmp -385
+jmp +1
+jmp -357
+acc -13
+acc -13
+jmp -360
+jmp -393
+acc +4
+nop -102
+jmp -316
+jmp -248
+acc +4
+nop -487
+jmp -339
+acc +3
+jmp -190
+acc +24
+acc +31
+jmp -166
+jmp -482
+acc +22
+acc +32
+jmp -290
+acc +22
+acc +48
+acc +5
+acc -6
+jmp -330
+nop -203
+acc +7
+acc +1
+jmp -287
+acc +15
+acc +3
+jmp -230
+acc +37
+nop -162
+jmp +33
+jmp -147
+acc +16
+acc +39
+acc +49
+jmp -560
+acc +26
+jmp +26
+jmp -283
+jmp -486
+acc -9
+jmp +1
+acc +25
+acc +1
+jmp -514
+acc +46
+jmp -166
+acc -5
+acc +35
+nop -204
+jmp -175
+nop -30
+nop +11
+jmp -400
+acc +15
+acc -7
+acc -1
+jmp +18
+acc +31
+acc +16
+acc +43
+acc +33
+jmp -260
+acc +1
+acc +23
+acc +25
+acc -1
+jmp -200
+acc -15
+jmp -314
+jmp -238
+jmp -75
+jmp -192
+acc +30
+jmp -525
+acc -14
+jmp +17
+acc +7
+acc +9
+acc -6
+nop -312
+jmp -559
+acc +28
+jmp -305
+jmp -239
+acc +0
+acc -5
+acc +9
+jmp -471
+nop -327
+acc -5
+acc -19
+jmp -496
+acc +17
+jmp +1
+jmp +1
+acc +29
+jmp +1