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2024/23
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‎2024/Day23/README.md

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## --- Day 23: LAN Party ---
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As The Historians wander around a secure area at Easter Bunny HQ, you come across posters for a [LAN party](https://en.wikipedia.org/wiki/LAN_party) scheduled for today! Maybe you can find it; you connect to a nearby _datalink port_ and download a map of the local network (your puzzle input).
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The network map provides a list of every <em>connection between two computers</em>. For example:
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_Visit the website for the full story and [full puzzle](https://adventofcode.com/2024/day/23) description._
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We tackled a graph algorithm problem today, where we had to find maximal cliques in an undirected graph. The literature provides [efficient algorithms](https://en.wikipedia.org/wiki/Bron%E2%80%93Kerbosch_algorithm) for this problem, but our graph is not too large, so we can use a straightforward "poor man's" strategy as well.
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I started by creating _seed_ components containing nodes that start with '_t_'. Then, I proceeded to _grow_ these components by adding a single node to them in all possible ways. First, I identify the neighbors of each _t_ node, followed by the triples which is required to solve Part 1. In Part 2, this process is continued until a single maximal component remains.

‎2024/Day23/Solution.cs

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namespace AdventOfCode.Y2024.Day23;
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using System;
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using System.Collections.Generic;
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using System.Collections.Immutable;
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using System.Linq;
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using Graph = System.Collections.Generic.Dictionary<string, System.Collections.Generic.HashSet<string>>;
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using Component = string;
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[ProblemName("LAN Party")]
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class Solution : Solver {
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public object PartOne(string input) {
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var g = GetGraph(input);
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var components = GetSeed(g);
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components = Grow(g, components);
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components = Grow(g, components);
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return components.Count;
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}
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public object PartTwo(string input) {
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var g = GetGraph(input);
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var components = GetSeed(g);
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while (components.Count > 1) {
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components = Grow(g, components);
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}
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return components.Single();
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}
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HashSet<Component> GetSeed(Graph g) => g.Keys.Where(k=>k.StartsWith("t")).ToHashSet();
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HashSet<Component> Grow(Graph g, HashSet<Component> components) => (
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from c in components
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let members = Members(c)
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from neighbour in members.SelectMany(m => g[m]).Distinct()
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where !members.Contains(neighbour)
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where members.All(m => g[neighbour].Contains(m))
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select Extend(c, neighbour)
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).ToHashSet();
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IEnumerable<string> Members(Component c) =>
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c.Split(",");
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Component Extend(Component c, string item) =>
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string.Join(",", Members(c).Append(item).OrderBy(x=>x));
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Graph GetGraph(string input) {
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var edges =
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from line in input.Split("\n")
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let nodes = line.Split("-")
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from edge in new []{(nodes[0], nodes[1]), (nodes[1], nodes[0])}
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select (From: edge.Item1, To: edge.Item2);
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return (
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from e in edges
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group e by e.From into g
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select (g.Key, g.Select(e => e.To).ToHashSet())
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).ToDictionary();
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}
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}

‎2024/Day23/illustration.jpeg

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‎2024/Day23/input.in

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‎2024/Day23/input.refout

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dd,ig,il,im,kb,kr,pe,ti,tv,vr,we,xu,zi

‎2024/SplashScreen.cs

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@@ -8,8 +8,8 @@ public void Show() {
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var color = Console.ForegroundColor;
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Write(0xcc00, false, " ▄█▄ ▄▄█ ▄ ▄ ▄▄▄ ▄▄ ▄█▄ ▄▄▄ ▄█ ▄▄ ▄▄▄ ▄▄█ ▄▄▄\n █▄█ █ █ █ █ █▄█ █ █ █ █ █ █▄ ");
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Write(0xcc00, false, " █ █ █ █ █ █▄█\n █ █ █▄█ ▀▄▀ █▄▄ █ █ █▄ █▄█ █ █▄ █▄█ █▄█ █▄▄ 0x0000 | 2024\n ");
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Write(0xcc00, false, " \n ");
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Write(0xcc00, false, " █ █ █ █ █ █▄█\n █ █ █▄█ ▀▄▀ █▄▄ █ █ █▄ █▄█ █ █▄ █▄█ █▄█ █▄▄ $year = 2024\n ");
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Write(0xcc00, false, "\n ");
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Write(0x888888, false, " .-----. .------------------. \n ");
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Write(0xcccccc, false, ".--'");
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Write(0xe3b585, false, "~ ~ ~");
@@ -49,9 +49,9 @@ public void Show() {
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Write(0xcccccc, false, "| 3 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "|");
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Write(0x488813, false, "@");
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Write(0x427322, false, "@");
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Write(0x5eabb4, false, "..");
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Write(0x4d8b03, false, "@");
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Write(0x1461f, false, "@");
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Write(0xe3b585, false, "'. ~ ");
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Write(0xcc00, false, "\" ' ");
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Write(0xe3b585, false, "~ ");
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Write(0xcccccc, false, "| 4 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "|");
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Write(0x4d8b03, false, "_");
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Write(0x427322, false, "_");
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Write(0x5eabb4, false, ".~.");
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Write(0x4d8b03, false, "_");
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Write(0x427322, false, "@");
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Write(0x4d8b03, false, "_@");
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Write(0xe3b585, false, "'.. ~ ~ ");
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Write(0xffff66, true, "*");
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Write(0xcccccc, false, "| | ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "| ");
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Write(0xffffff, false, "||| ");
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Write(0x1461f, false, "#");
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Write(0x1461f, false, "@");
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Write(0x427322, false, "@");
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Write(0x488813, false, "@ ");
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Write(0x7fbd39, false, "@");
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Write(0x4d8b03, false, "@");
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Write(0xe3b585, false, "'''...");
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Write(0xcccccc, false, "| |");
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Write(0xa25151, false, "... ");
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Write(0xcccccc, false, "| 6 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "|");
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Write(0x488813, false, "#");
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Write(0x427322, false, "#");
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Write(0xffffff, false, "~~~");
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Write(0x488813, false, "#");
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Write(0x427322, false, "@");
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Write(0x7fbd39, false, "@");
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Write(0x4d8b03, false, "@#");
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Write(0x488813, false, "@#@");
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Write(0x1461f, false, "@");
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Write(0x427322, false, "@ ");
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Write(0x4d8b03, false, "# ");
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Write(0x7fbd39, false, "@");
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Write(0x488813, false, "@ ");
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Write(0xcccccc, false, "| |");
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Write(0xa5a8af, false, "/\\ ");
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Write(0xa25151, false, "''. ");
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Write(0xa5a8af, false, "/\\ ");
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Write(0xa25151, false, "..' ");
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Write(0xcccccc, false, "| | ");
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Write(0xffffff, false, ". ");
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Write(0xffffff, false, ". ");
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Write(0xb5ed, false, ". ");
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Write(0xcccccc, false, "| 11 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "| ");
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Write(0x333333, false, "::");
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Write(0xffff66, true, ":");
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Write(0x333333, false, "::");
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Write(0xcccccc, false, "| |");
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Write(0xa2db, false, ". ");
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Write(0xffffff, false, ". ");
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Write(0xa2db, false, ".");
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Write(0xcccccc, false, "| | ");
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Write(0xffffff, false, ". ");
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Write(0xa2db, false, ". . ");
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Write(0xcccccc, false, "| 12 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "|");
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Write(0xcc00, false, "...");
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Write(0xffffff, false, "'..''");
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Write(0xcccccc, false, "| |");
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Write(0xffffff, true, ". ");
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Write(0x333333, false, ":");
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Write(0xffffff, true, ". ");
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Write(0x333333, false, ".:");
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Write(0x9900, true, ":::");
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Write(0x333333, false, ":");
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Write(0xcccccc, false, "| |");
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Write(0x5555bb, false, "~ ");
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Write(0xcc00, false, ":");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, " '. ");
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Write(0x333333, false, ". ");
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Write(0x666666, false, " '. ");
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Write(0x333333, false, ". ");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, "┬o┤ten├─");
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Write(0xcccccc, false, "| 17 ");
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Write(0xcc00, false, "'..' .'");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, " '");
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Write(0x456efe, true, "o ");
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Write(0x333333, false, ". ");
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Write(0x456efe, true, "o ");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, "┘");
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Write(0xffff66, true, "*");
@@ -254,7 +252,9 @@ public void Show() {
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Write(0x5555bb, false, "~ ");
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Write(0xcc00, false, "..' ");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, ": '. ");
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Write(0x666666, false, ":");
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Write(0x333333, false, ".");
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Write(0x666666, false, " '. ");
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Write(0xcccccc, false, "| |");
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Write(0x666666, false, "─┘├┬┬┬┴─");
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Write(0xcccccc, false, "| 19 ");
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Write(0x66ff, true, "O");
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Write(0xcccccc, false, "| 22 ");
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Write(0xffff66, false, "**\n ");
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Write(0xcccccc, false, "|");
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Write(0xff0000, false, "/ ");
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Write(0x880000, false, "/ ");
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Write(0xff0000, false, "/\\|");
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Write(0x66ff, false, "| | )");
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Write(0xaaaaaa, false, "/");
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Write(0xe6410b, false, "~");
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Write(0xaaaaaa, false, "\\ ");
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Write(0xcccccc, false, "| |");
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Write(0x66ff, false, "___");
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Write(0xff0000, false, "|");
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Write(0xcccccc, false, "\\|");
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Write(0x66ff, false, "________");
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Write(0x9900, false, ">");
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Write(0x66ff, true, "O");
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Write(0x9900, false, ">>");
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Write(0xff9900, true, "o");
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Write(0x9900, false, ">>");
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Write(0xff9900, true, "o");
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Write(0xcccccc, false, "| 23 ");
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Write(0xffff66, false, "**\n ");
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Write(0x333333, false, "| | | | ");
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Write(0x666666, false, "23\n 24\n ");
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Write(0x666666, false, " 25\n \n");
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Write(0x666666, false, "24\n 25\n \n");
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Console.ForegroundColor = color;
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Console.WriteLine();

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