day13 part 1

aoc2020.test/DayTests.cs

@@ -20,6 +20,7 @@ namespace aoc2020.test
         [DataRow(typeof(Day10), "1980", "4628074479616")]
         [DataRow(typeof(Day11), "2303", "2057")]
         [DataRow(typeof(Day12), "1710", "62045")]
+        [DataRow(typeof(Day13), "171", "")]
         public void CheckAllDays(Type dayType, string part1, string part2)
         {
             // create day instance

aoc2020/Day13.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace aoc2020
+{
+    /// <summary>
+    ///     Day 13: <see href="https://adventofcode.com/2020/day/13">Shuttle Search</see>
+    /// </summary>
+    public sealed class Day13 : Day
+    {
+        private readonly long _earliest;
+        private readonly string[] _fullSchedule;
+        private readonly long[] _buses;
+
+        public Day13() : base(13)
+        {
+            _earliest = long.Parse(Input.First());
+            _fullSchedule = Input.Last().Split(',');
+            _buses = _fullSchedule.Where(c => c != "x").Select(long.Parse).ToArray();
+        }
+
+        public override string Part1()
+        {
+            for (var i = _earliest; ; i++)
+            {
+                if (_buses.Any(b => i % b == 0))
+                {
+                    var bus = _buses.First(b => i % b == 0);
+                    return $"{bus * (i - _earliest)}";
+                }
+            }
+        }
+
+        public override string Part2()
+        {
+            return "";
+        }
+    }
+}

aoc2020/input/day13.in

@@ -0,0 +1,2 @@
+1000417
+23,x,x,x,x,x,x,x,x,x,x,x,x,41,x,x,x,37,x,x,x,x,x,479,x,x,x,x,x,x,x,x,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,373,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,19