From 184c3ede8bddb620e7da07341a72ac692a8925ab Mon Sep 17 00:00:00 2001
From: Ben Harris <ben@tilde.team>
Date: Wed, 4 Dec 2019 11:32:43 -0500
Subject: [PATCH] day 4

---
 Day4.cs        | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
 DayFactory.cs  |  3 ++-
 aoc2019.csproj |  3 +++
 input/day4.in  |  1 +
 4 files changed, 69 insertions(+), 1 deletion(-)
 create mode 100644 Day4.cs
 create mode 100644 input/day4.in

diff --git a/Day4.cs b/Day4.cs
new file mode 100644
index 0000000..8e57b00
--- /dev/null
+++ b/Day4.cs
@@ -0,0 +1,63 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace aoc2019
+{
+    internal class Day4 : Day
+    {
+        int start, end;
+
+        public Day4()
+        {
+            var range = File.ReadLines("input/day4.in")
+                .First()
+                .Split('-')
+                .Select(i => int.Parse(i))
+                .ToList();
+
+            start = range[0]; end = range[1];
+        }
+
+        private bool IsValid(int i)
+        {
+            return Math.Floor(Math.Log10(i) + 1) == 6
+                && i >= start
+                && i <= end
+                && IsIncreasingDigits(i);
+        }
+
+        private bool IsIncreasingDigits(int i)
+        {
+            int prev = 0;
+            bool hasDup = false;
+            foreach (var c in i.ToString())
+            {
+                int curr = c - '0';
+                if (curr < prev)
+                    return false;
+                if (curr == prev)
+                    hasDup = true;
+                prev = curr;
+            }
+            return hasDup;
+        }
+
+        private bool Part2Criterion(int i)
+        {
+            var s = i.ToString();
+            return s.Select(c => s.Count(j => j == c)).Any(c => c == 2);
+        }
+
+        public override void Part1()
+        {
+            Console.WriteLine(Enumerable.Range(start, end).Count(i => IsValid(i)));
+        }
+
+        public override void Part2()
+        {
+            Console.WriteLine(Enumerable.Range(start,end).Count(i => IsValid(i) && Part2Criterion(i)));
+        }
+    }
+}
diff --git a/DayFactory.cs b/DayFactory.cs
index 5938d75..0a05ecb 100644
--- a/DayFactory.cs
+++ b/DayFactory.cs
@@ -11,8 +11,9 @@ namespace aoc2019
                 case 1: return new Day1();
                 case 2: return new Day2();
                 case 3: return new Day3();
+                case 4: return new Day4();
                 default: return null;
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/aoc2019.csproj b/aoc2019.csproj
index f45d1e6..1533700 100644
--- a/aoc2019.csproj
+++ b/aoc2019.csproj
@@ -15,6 +15,9 @@
     <None Update="input\day3.in">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="input\day4.in">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
   </ItemGroup>
 
 </Project>
diff --git a/input/day4.in b/input/day4.in
new file mode 100644
index 0000000..6190bcb
--- /dev/null
+++ b/input/day4.in
@@ -0,0 +1 @@
+245318-765747