From 74283d420c4448218e744dffe0f92e86476454f5 Mon Sep 17 00:00:00 2001
From: Tadej Koderman <tadej.koderman@docentric.com>
Date: Wed, 4 Dec 2024 06:43:16 +0100
Subject: [PATCH] Day 4

---
 AoCCore/Extensions.cs |   8 ++-
 AoCCore/Y2024.cs      | 122 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 125 insertions(+), 5 deletions(-)

diff --git a/AoCCore/Extensions.cs b/AoCCore/Extensions.cs
index 1b7ae32..6eb3b8f 100644
--- a/AoCCore/Extensions.cs
+++ b/AoCCore/Extensions.cs
@@ -1,4 +1,5 @@
-using System.Linq.Expressions;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq.Expressions;
 using System.Runtime.CompilerServices;
 
 namespace AoCCore;
@@ -51,4 +52,9 @@ public static void P<T>(this IEnumerable<T> values, string message)
     public static long Long(this string input) => input.As<long>();
 
     public static string Join(this IEnumerable<string> input, string separator = ",") => string.Join(separator, input);
+
+    public static MatchCollection Matches(this string input, [StringSyntax("Regex")] string pattern)
+    {
+        return new Regex(pattern).Matches(input);
+    }
 }
\ No newline at end of file
diff --git a/AoCCore/Y2024.cs b/AoCCore/Y2024.cs
index be76b46..256181f 100644
--- a/AoCCore/Y2024.cs
+++ b/AoCCore/Y2024.cs
@@ -129,8 +129,9 @@ static bool IsSafe(int[] report)
     */
     public static void Day03A()
     {
-        new Regex(@"mul\((\d+),(\d+)\)")
-            .Matches(Read.StringBatch().Join())
+        Read.StringBatch()
+            .Join()
+            .Matches(@"mul\((\d+),(\d+)\)")
             .Sum(m => m.Groups[1].Value.Long() * m.Groups[2].Value.Int())
             .P("Sum");
 
@@ -143,8 +144,9 @@ public static void Day03A()
     */
     public static void Day03B()
     {
-        new Regex(@"mul\((\d+),(\d+)\)|(do\(\))|(don't\(\))")
-            .Matches(string.Join(",", Read.StringBatch()))
+        Read.StringBatch()
+            .Join()
+            .Matches(@"mul\((\d+),(\d+)\)|(do\(\))|(don't\(\))")
             .Aggregate(
                 (Sum: 0L, Enabled: true),
                 (a, m) => m.Groups[3].Success
@@ -160,6 +162,118 @@ public static void Day03B()
         // 80570939
     }
 
+    /*
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
+
+    */
+    public static void Day04A()
+    {
+        var input = Read.StringBatch().ToArray();
+
+        var h = input.Length; if (h == 0) return;
+        var w = input[0].Length;
+
+        var count = 0;
+
+        for (int i = 0; i < h; i++)
+        {
+            for (int j = 0; j < w; j++)
+            {
+                if (input[i][j] != 'X')
+                    continue;
+
+                if (All(1, 0)) count++;     // D
+                if (All(1, 1)) count++;     // DR
+                if (All(0, 1)) count++;     //  R
+                if (All(-1, 1)) count++;    // UR
+                if (All(-1, 0)) count++;    // U
+                if (All(-1, -1)) count++;   // UL
+                if (All(0, -1)) count++;    //  L
+                if (All(1, -1)) count++;    // DL
+
+                bool All(int y, int x)
+                {
+                    return Check(1 * y, 1 * x, 'M')
+                        && Check(2 * y, 2 * x, 'A')
+                        && Check(3 * y, 3 * x, 'S');
+                }
+
+                bool Check(int y, int x, char c)
+                {
+                    return i + y >= 0
+                        && i + y < h
+                        && j + x >= 0
+                        && j + x < w
+                        && input[i + y][j + x] == c;
+                }
+            }
+        }
+
+        count.P();
+    }
+
+    public static void Day04B()
+    {
+        var input = Read.StringBatch().ToArray();
+
+        var h = input.Length; if (h == 0) return;
+        var w = input[0].Length;
+
+        var count = 0;
+
+        for (int i = 0; i < h; i++)
+        {
+            for (int j = 0; j < w; j++)
+            {
+                if (input[i][j] != 'M')
+                    continue;
+
+                // if (All(1, 0)) count++;     // D
+                if (All(1, 1)) count++;     // DR
+                // if (All(0, 1)) count++;     //  R
+                if (All(-1, 1)) count++;    // UR
+                // if (All(-1, 0)) count++;    // U
+                if (All(-1, -1)) count++;   // UL
+                // if (All(0, -1)) count++;    //  L
+                if (All(1, -1)) count++;    // DL
+
+                bool All(int y, int x)
+                {
+                    return Check(1 * y, 1 * x, 'A')
+                        && Check(2 * y, 2 * x, 'S')
+                        &&
+                        (
+                            Check(2 * y, 0 * x, 'M')
+                            && Check(0 * y, 2 * x, 'S')
+                        ||
+                            Check(2 * y, 0 * x, 'S')
+                            && Check(0 * y, 2 * x, 'M')
+                        );
+                }
+
+                bool Check(int y, int x, char c)
+                {
+                    return i + y >= 0
+                        && i + y < h
+                        && j + x >= 0
+                        && j + x < w
+                        && input[i + y][j + x] == c;
+                }
+            }
+        }
+
+        (count / 2).P();
+    }
+
     public static void Current() // Day05A()
     {
     }