day1 init

.gitignore

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+*.swp
+*.*~
+project.lock.json
+.DS_Store
+*.pyc
+
+# Visual Studio Code
+.vscode
+
+# User-specific files
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+
+# Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleases/
+x64/
+x86/
+build/
+bld/
+[Bb]in/
+[Oo]bj/
+msbuild.log
+msbuild.err
+msbuild.wrn
+
+# Visual Studio 2015
+.vs/

Day1.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace aoc2019
+{
+    public class Day1
+    {
+        private static IEnumerable<int> lines = 
+            File.ReadLines("input/day1.in").Select(line => int.Parse(line));
+
+        private static int FuelCost(int weight) => weight / 3 - 2;
+
+        public static void Part1()
+        {
+            Console.WriteLine(lines.Select(num => FuelCost(num)).Sum());
+        }
+
+        private static int FullCost(int cost)
+        {
+            int total = 0, newcost = 0, tmp = cost;
+
+            while ((newcost = FuelCost(tmp)) >= 0)
+            {
+                total += newcost;
+                tmp = newcost;
+            }
+
+            return total;
+        }
+
+        public static void Part2()
+        {
+            Console.WriteLine(lines.Select(cost => FullCost(cost)).Sum());
+        }
+    }
+}
+

Program.cs

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+using System;
+using System.IO;
+using System.Linq;
+
+namespace aoc2019
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Day1.Part1();
+            Day1.Part2();
+        }
+    }
+}

aoc2019.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>

input/day1.in

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