From 5b25791bee90f48264a64b6d5930cef94c3dc255 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bal=C3=A1zs=20Zaicsek?= <zebalu@gmail.com>
Date: Wed, 13 Dec 2023 07:43:44 +0100
Subject: [PATCH] Day13

---
 .../io/github/zebalu/aoc2023/days/Day13.java  | 151 ++++++++++++++++++
 1 file changed, 151 insertions(+)
 create mode 100644 aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day13.java

diff --git a/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day13.java b/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day13.java
new file mode 100644
index 0000000..5c457d1
--- /dev/null
+++ b/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day13.java
@@ -0,0 +1,151 @@
+package io.github.zebalu.aoc2023.days;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+public class Day13 {
+    public static void main(String[] args) {
+        String input = readInput();
+        String[] patterns = input.split("\n\n");
+        List<Maze> mazes = Arrays.stream(patterns).map(p->new Maze(p.lines().toList())).toList();
+        System.out.println(mazes.stream().mapToInt(Maze::findAnyMirror).sum());
+        System.out.println(mazes.stream().mapToInt(Maze::findAnyMirrorWith1Diff).sum());
+    }
+
+    private static String readInput() {
+        try {
+            return Files.readString(Path.of("day13.txt").toAbsolutePath());
+        } catch (Exception e) {
+            throw new IllegalStateException(e);
+        }
+    }
+    
+    private record Maze(List<String> lines) {
+        int findVerticalMirror() {
+            for(int i = 0; i<lines.getFirst().length()-1; ++i) {
+                boolean match = true;
+                for(int y=0; y<lines.size() && match; ++y) {
+                    match = checkPosinLine(i, lines.get(y));
+                }
+                if(match) {
+                    return i+1;
+                }
+            }
+            return -1;
+        }
+        
+        int findHorizontalMirror() {
+            for(int i = 0; i<lines.size()-1; ++i) {
+                if(compareLines(i)) {
+                    return i+1;
+                }
+            }
+            return -1;
+        }
+        
+        int findAnyMirror() {
+            int i = findHorizontalMirror();
+            if(i>0) {
+                return i*100;
+            }
+            i = findVerticalMirror();
+            if(i>0) {
+                return i;
+            }
+            throw new NoSuchElementException();
+        }
+        
+        int findVerticalMirrorWith1Diff() {
+            for(int i = 0; i<lines.getFirst().length()-1; ++i) {
+                int diff = 0;
+                for(int y=0; y<lines.size() && diff<2; ++y) {
+                    diff += checkPosinLineWith1Diff(i, lines.get(y));
+                }
+                if(diff == 1) {
+                    return i+1;
+                }
+            }
+            return -1;
+        }
+        
+        int findHorizontalMirrorWith1Diff() {
+            for(int i = 0; i<lines.size()-1; ++i) {
+                if(compareLinesWith1Diff(i)) {
+                    return (i+1);
+                }
+            }
+            return -1;
+        }
+        
+        int findAnyMirrorWith1Diff() {
+            int i = findHorizontalMirrorWith1Diff();
+            if(i>0) {
+                return i*100;
+            }
+            i = findVerticalMirrorWith1Diff();
+            if(i>0) {
+                return i;
+            }
+            throw new NoSuchElementException();
+        }
+        
+        private boolean checkPosinLine(int pos, String line) {
+            int i = pos;
+            int j = pos+1;
+            boolean match = true;
+            while(match && i>=0 && j < line.length()) {
+                match = line.charAt(i) == line.charAt(j);
+                --i;
+                ++j;
+            }
+            return match;
+        }
+        
+        private boolean compareLines(int lineCount) {
+            int i = lineCount;
+            int j = lineCount+1;
+            boolean match = true;
+            while( match && i>=0 && j<lines.size()) {
+                for(int x=0; x<lines.get(i).length() && match; ++x) {
+                    match = lines.get(i).charAt(x) == lines.get(j).charAt(x);
+                }
+                --i;
+                ++j;
+            }
+            return match;
+        }
+        
+        private int checkPosinLineWith1Diff(int pos, String line) {
+            int i = pos;
+            int j = pos+1;
+            int diff = 0;
+            while(i>=0 && j < line.length() && diff<2) {
+                if(line.charAt(i) != line.charAt(j)) {
+                    ++diff;
+                }
+                --i;
+                ++j;
+            }
+            return diff;
+        }
+        
+        private boolean compareLinesWith1Diff(int lineCount) {
+            int i = lineCount;
+            int j = lineCount+1;
+            int diffCount = 0;
+            while( i>=0 && j<lines.size()) {
+                for(int x=0; x<lines.get(i).length() && diffCount<2; ++x) {
+                    if(lines.get(i).charAt(x) != lines.get(j).charAt(x)) {
+                        ++diffCount;
+                    }
+                }
+                --i;
+                ++j;
+            }
+            return diffCount == 1;
+        }
+    }
+}