diff --git a/2020/Day09.cs b/2020/Day09.cs new file mode 100644 index 0000000..039f0c2 --- /dev/null +++ b/2020/Day09.cs @@ -0,0 +1,76 @@ +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 Day09 { + + static bool Valid(List ints, int preambleSize, int target) { + for (int i = target - preambleSize; i < target - 1; i++) { + for (int j = i + 1; j < target; j++) { + if (i == j) { + continue; + } + if (ints[i] + ints[j] == ints[target]) { + return true; + } + } + } + return false; + } + + static long FindInvalid(List ints, int preambleSize) { + for (int target = preambleSize; target < ints.Count(); target++) { + if (!Valid(ints, preambleSize, target)) { + return ints[target]; + } + } + throw new Exception("didn't find an invalid int"); + } + + static long Part1() { + string[] input = File.ReadAllLines(Util.RootDir + "day09.txt"); + List ints = input.ToList().Select(long.Parse).ToList(); + return FindInvalid(ints, 25); + } + + static int Part2() { + return -1; + } + + [Fact] + public static void Test() { + string[] example = +@"35 +20 +15 +25 +47 +40 +62 +55 +65 +95 +102 +117 +150 +182 +127 +219 +299 +277 +309 +576".Split('\n'); + List ints = example.ToList().Select(long.Parse).ToList(); + Assert.Equal(127, FindInvalid(ints, 5)); + + Assert.Equal(50047984, Part1()); + Assert.Equal(-1, Part2()); + } + } +} diff --git a/2020/day09.txt b/2020/day09.txt new file mode 100644 index 0000000..2de9dba --- /dev/null +++ b/2020/day09.txt @@ -0,0 +1,1000 @@ +37 +1 +33 +42 +17 +34 +27 +44 +26 +39 +3 +43 +30 +22 +9 +38 +7 +28 +21 +4 +50 +14 +35 +12 +5 +6 +71 +8 +15 +10 +11 +13 +16 +53 +17 +20 +18 +19 +23 +24 +9 +22 +25 +26 +21 +27 +28 +14 +67 +29 +30 +31 +33 +59 +32 +34 +35 +37 +40 +42 +54 +41 +39 +36 +23 +51 +61 +58 +43 +44 +102 +47 +46 +52 +53 +78 +55 +56 +65 +57 +101 +66 +114 +59 +80 +64 +62 +67 +69 +79 +87 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