You resume walking through the valley of mirrors and - <em>SMACK!</em> - run directly into one. Hopefully nobody was watching, because that must have been pretty embarrassing.

Upon closer inspection, you discover that every mirror has exactly one <em>smudge</em>: exactly one <code>.</code> or <code>#</code> should be the opposite type.

In each pattern, you'll need to locate and fix the smudge that causes a <em>different reflection line</em> to be valid. (The old reflection line won't necessarily continue being valid after the smudge is fixed.)

Here's the above example again:

<pre>

<code>#.##..##.

..#.##.#.

##......#

##......#

..#.##.#.

..##..##.

#.#.##.#.

#...##..#

#....#..#

..##..###

#####.##.

#####.##.

..##..###

#....#..#

</code>

</pre>

The first pattern's smudge is in the top-left corner. If the top-left <code>#</code> were instead <code>.</code>, it would have a different, horizontal line of reflection:

<pre>

<code>1 ..##..##. 1

2 ..#.##.#. 2

3v##......#v3

4^##......#^4

5 ..#.##.#. 5

6 ..##..##. 6

7 #.#.##.#. 7

</code>

</pre>

With the smudge in the top-left corner repaired, a new horizontal line of reflection between rows 3 and 4 now exists. Row 7 has no corresponding reflected row and can be ignored, but every other row matches exactly: row 1 matches row 6, row 2 matches row 5, and row 3 matches row 4.

In the second pattern, the smudge can be fixed by changing the fifth symbol on row 2 from <code>.</code> to <code>#</code>:

<pre>

<code>1v#...##..#v1

2^#...##..#^2

3 ..##..### 3

4 #####.##. 4

5 #####.##. 5

6 ..##..### 6

7 #....#..# 7

</code>

</pre>

Now, the pattern has a different horizontal line of reflection between rows 1 and 2.

Summarize your notes as before, but instead use the new different reflection lines. In this example, the first pattern's new horizontal line has 3 rows above it and the second pattern's new horizontal line has 1 row above it, summarizing to the value <code><em>400</em></code>.

In each pattern, fix the smudge and find the different line of reflection. <em>What number do you get after summarizing the new reflection line in each pattern in your notes?</em>

using adventofcode.Utils;

// Thx to https://github.com/dpvdberg/aoc2023/blob/master/AdventOfCode2023/Days/Day13/Day13Solution.cs

// Elegant solution, I was trying to do something similar but I was not able to get it to work

private readonly Dictionary<int, (int num, bool isHorizontal)> mirrors = new();

var blocks = ParseBlocks(input);

var result = 0;

for (var i = 0; i < blocks.Length; i++)

{

TryFindMirror(blocks[i], i, out var res);

result += res;

}

return result;

}

private void TryFindMirror(string block, int key, out int result)

{

var lines = block.Split("\n", StringSplitOptions.RemoveEmptyEntries);

var columns = block.SplitIntoColumns().ToList();

for (var i = 1; i < lines.Length; i++)

{

if (lines.Take(i).Reverse().Zip(lines.Skip(i)).All(x => x.First == x.Second))

{

if (mirrors.TryGetValue(key, out (int num, bool isHorizontal) value))

{

if (value.isHorizontal && value.num == i) continue;

}

mirrors[key] = (i, true);

result = i * 100;

return;

}

}

for (var i = 1; i < columns.Count; i++)

{

if (columns.Take(i).Reverse().Zip(columns.Skip(i)).All(x => x.First == x.Second))

{

if (mirrors.TryGetValue(key, out (int num, bool isRow) value))

{

if (!value.isRow && value.num == i) continue;

}

mirrors[key] = (i, false);

result = i;

return;

}

}

result = 0;

private static string[] ParseBlocks(string input) =>

input.Split("\n\n", StringSplitOptions.RemoveEmptyEntries);

27742

Write(0xcc00, false, " █ █ █ █ █ █▄█\n █ █ █▄█ ▀▄▀ █▄▄ █ █ █▄ █▄█ █ █▄ █▄█ █▄█ █▄▄ int y = 2023;\n ");

Write(0xcc00, false, " \n ");

Write(0x666666, false, " . * ");

Write(0x666666, false, "**\n . * ");

Write(0x666666, false, " . . . ' * ");

Write(0x666666, false, "'. './\\*/\\ ~ ");

Write(0xffff66, false, "*");

Write(0x666666, false, "*\n ");

Write(0x666666, false, " * '.. /\\ ");

Write(0xd4dde4, false, ".'''. '");

Write(0x666666, false, "'''.... .. . ' ");

Write(0x666666, false, " * ");

Write(0xcccccc, false, "19 ");

Write(0x666666, false, "**\n ");

Write(0xe3b585, false, "~ ~ ~");

Write(0x666666, false, " * ");

Write(0xe3b585, false, ".' ");

Write(0xcccccc, false, "20 ");

Write(0x666666, false, "**\n ");

Write(0xe3b585, false, "'.. ~ ~ ");

Write(0xcc00, false, "'");

Write(0x333333, false, "* ");

Write(0xcc00, false, "'.");

Write(0xcc00, false, "'. ");

Write(0x666666, false, "21\n ");

Write(0xcc00, false, ": ");