123 lines
3.5 KiB
C#
123 lines
3.5 KiB
C#
using System;
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using static System.Console;
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using System.Collections.Generic;
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using System.IO;
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using System.Linq;
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using System.Text.RegularExpressions;
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using Xunit;
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namespace AdventOfCode {
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public class Day08 {
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public class GameConsole {
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int accumulator = 0;
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int pointer = 0;
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// Returns a (bool, int) tuple, where the bool indicates whether the program terminated
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// normally (if false, it executed an infinite loop), and the int indicates the value of
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// the accumulator at the time of termination.
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public (bool, int) Execute(List<Instruction> code) {
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var instructionsExecuted = new HashSet<int>();
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while (pointer < code.Count()) {
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if (instructionsExecuted.Contains(pointer)) {
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return (false, accumulator); // loop detected
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}
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instructionsExecuted.Add(pointer);
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Instruction instruction = code[pointer];
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switch (instruction.Op) {
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case "nop":
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pointer++;
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break;
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case "acc":
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pointer++;
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accumulator += instruction.Value;
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break;
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case "jmp":
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pointer += instruction.Value;
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break;
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default:
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throw new Exception("invalid op");
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}
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}
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return (true, accumulator); // normal termination
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}
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}
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public record Instruction(string Op, int Value);
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public static int RepairBrokenInstruction(List<Instruction> code) {
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for (int i = 0; i < code.Count(); i++) {
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if (code[i].Op == "acc") {
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continue; // this line can't be the broken one
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}
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List<Instruction> repaired = new List<Instruction>(code);
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if (repaired[i].Op == "nop") {
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repaired[i] = new Instruction("jmp", repaired[i].Value);
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} else {
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repaired[i] = new Instruction("nop", repaired[i].Value);
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}
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var (success, result) = new GameConsole().Execute(repaired);
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if (success) {
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return result;
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}
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}
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throw new Exception("didn't find a valid instruction to repair");
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}
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static List<Instruction> ParseInstructions(string[] code) {
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var result = new List<Instruction>();
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foreach (string line in code) {
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string[] tokens = line.Split(' ');
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result.Add(new Instruction(tokens[0], int.Parse(tokens[1])));
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}
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return result;
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}
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static int Part1() {
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string[] input = File.ReadAllLines(Util.RootDir + "day08.txt");
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List<Instruction> code = ParseInstructions(input);
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(bool finished, int result) = new GameConsole().Execute(code);
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return result;
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}
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static int Part2() {
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string[] input = File.ReadAllLines(Util.RootDir + "day08.txt");
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List<Instruction> code = ParseInstructions(input);
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return RepairBrokenInstruction(code);
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}
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[Fact]
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public static void Test() {
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string[] example =
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@"nop +0
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acc +1
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jmp +4
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acc +3
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jmp -3
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acc -99
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acc +1
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jmp -4
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acc +6".Split('\n');
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List<Instruction> parsed = ParseInstructions(example);
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Assert.Equal(9, parsed.Count());
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Assert.Equal((false, 5), new GameConsole().Execute(parsed));
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Assert.Equal(1610, Part1());
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string[] example2 =
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@"nop +0
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acc +1
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jmp +4
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acc +3
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jmp -3
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acc -99
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acc +1
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nop -4
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acc +6".Split('\n');
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List<Instruction> parsed2 = ParseInstructions(example2);
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Assert.Equal((true, 8), new GameConsole().Execute(parsed2));
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Assert.Equal(1703, Part2());
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}
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}
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}
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