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annotate day10.txt @ 19:1e16a25a9553

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Strip down the text to just the puzzle, not the fluff
author IBBoard <dev@ibboard.co.uk>
date Mon, 11 Dec 2023 20:38:55 +0000
parents 92144824cbb7
children
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9b1d04091335 Path finding through the pipes for day 10
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1 --- Day 10: Pipe Maze ---
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2
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3 You are in an area filled with pipes/paths. Your puzzle input is a map of the path of those pipes.
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4
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5 The pipes are arranged in a two-dimensional grid of tiles:
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6
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7 | is a vertical pipe connecting north and south.
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8 - is a horizontal pipe connecting east and west.
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9 L is a 90-degree bend connecting north and east.
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10 J is a 90-degree bend connecting north and west.
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11 7 is a 90-degree bend connecting south and west.
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12 F is a 90-degree bend connecting south and east.
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13 . is ground; there is no pipe in this tile.
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14 S is the starting position; there is a pipe on this tile, but your sketch doesn't show what shape the pipe has.
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15
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16 There is at least one continuous loop. You want to get to the point that is furthest around the path from the start point.
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17
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18 For example, here is a square loop of pipe:
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20 .....
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21 .F-7.
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22 .|.|.
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23 .L-J.
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24 .....
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25
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26 If the start is in the northwest corner, the sketch would instead look like this:
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27
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28 .....
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29 .S-7.
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30 .|.|.
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31 .L-J.
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32 .....
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33
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34 In the above diagram, the S tile is still a 90-degree F bend: you can tell because of how the adjacent pipes connect to it.
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35
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36 Unfortunately, there are also many pipes that aren't connected to the loop! This sketch shows the same loop as above:
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37
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38 -L|F7
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39 7S-7|
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40 L|7||
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41 -L-J|
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42 L|-JF
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43
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44 In the above diagram, you can still figure out which pipes form the main loop: they're the ones connected to S, pipes those pipes connect to, pipes those pipes connect to, and so on. Every pipe in the main loop connects to its two neighbors (including S, which will have exactly two pipes connecting to it, and which is assumed to connect back to those two pipes).
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45
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46 Here is a sketch that contains a slightly more complex main loop:
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47
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48 ..F7.
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49 .FJ|.
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50 SJ.L7
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51 |F--J
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52 LJ...
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53
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54 Here's the same example sketch with the extra, non-main-loop pipe tiles also shown:
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55
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56 7-F7-
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57 .FJ|7
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58 SJLL7
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59 |F--J
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60 LJ.LJ
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61
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62 When measuring the distance in the first example with the square loop:
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63
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64 .....
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65 .S-7.
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66 .|.|.
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67 .L-J.
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68 .....
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69
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70 You can count the distance each tile in the loop is from the starting point like this:
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71
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72 .....
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73 .012.
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74 .1.3.
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75 .234.
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76 .....
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77
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78 In this example, the farthest point from the start is 4 steps away.
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79
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80 Here's the more complex loop again:
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81
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82 ..F7.
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83 .FJ|.
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84 SJ.L7
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85 |F--J
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86 LJ...
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87
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88 Here are the distances for each tile on that loop:
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89
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90 ..45.
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91 .236.
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92 01.78
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93 14567
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94 23...
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95
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96 Find the single giant loop starting at S. How many steps along the loop does it take to get from the starting position to the point farthest from the starting position?
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97
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98 --- Part Two ---
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99
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100 Maybe there is something enclosed within the loops of the path? You need to calculate how many tiles are contained within the loop. For example:
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101
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102 ...........
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103 .S-------7.
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104 .|F-----7|.
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105 .||.....||.
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106 .||.....||.
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107 .|L-7.F-J|.
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108 .|..|.|..|.
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109 .L--J.L--J.
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110 ...........
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111
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112 The above loop encloses merely four tiles - the two pairs of . in the southwest and southeast (marked I below). The middle . tiles (marked O below) are not in the loop. Here is the same loop again with those regions marked:
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113
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114 ...........
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115 .S-------7.
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116 .|F-----7|.
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117 .||OOOOO||.
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118 .||OOOOO||.
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119 .|L-7OF-J|.
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120 .|II|O|II|.
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121 .L--JOL--J.
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122 .....O.....
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123
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124 In fact, there doesn't even need to be a full tile path to the outside for tiles to count as outside the loop - squeezing between pipes is also allowed! Here, I is still within the loop and O is still outside the loop:
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125
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126 ..........
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127 .S------7.
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128 .|F----7|.
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129 .||OOOO||.
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130 .||OOOO||.
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131 .|L-7F-J|.
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132 .|II||II|.
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133 .L--JL--J.
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134 ..........
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135
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136 In both of the above examples, 4 tiles are enclosed by the loop.
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137
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138 Here's a larger example:
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139
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140 .F----7F7F7F7F-7....
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141 .|F--7||||||||FJ....
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142 .||.FJ||||||||L7....
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143 FJL7L7LJLJ||LJ.L-7..
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144 L--J.L7...LJS7F-7L7.
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145 ....F-J..F7FJ|L7L7L7
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146 ....L7.F7||L7|.L7L7|
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147 .....|FJLJ|FJ|F7|.LJ
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148 ....FJL-7.||.||||...
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149 ....L---J.LJ.LJLJ...
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150
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151 The above sketch has many random bits of ground, some of which are in the loop (I) and some of which are outside it (O):
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152
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153 OF----7F7F7F7F-7OOOO
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154 O|F--7||||||||FJOOOO
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155 O||OFJ||||||||L7OOOO
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156 FJL7L7LJLJ||LJIL-7OO
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157 L--JOL7IIILJS7F-7L7O
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158 OOOOF-JIIF7FJ|L7L7L7
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159 OOOOL7IF7||L7|IL7L7|
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160 OOOOO|FJLJ|FJ|F7|OLJ
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161 OOOOFJL-7O||O||||OOO
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162 OOOOL---JOLJOLJLJOOO
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163
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164 In this larger example, 8 tiles are enclosed by the loop.
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165
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166 Any tile that isn't part of the main loop can count as being enclosed by the loop. Here's another example with many bits of junk pipe lying around that aren't connected to the main loop at all:
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167
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168 FF7FSF7F7F7F7F7F---7
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169 L|LJ||||||||||||F--J
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170 FL-7LJLJ||||||LJL-77
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171 F--JF--7||LJLJ7F7FJ-
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172 L---JF-JLJ.||-FJLJJ7
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173 |F|F-JF---7F7-L7L|7|
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174 |FFJF7L7F-JF7|JL---7
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175 7-L-JL7||F7|L7F-7F7|
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176 L.L7LFJ|||||FJL7||LJ
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177 L7JLJL-JLJLJL--JLJ.L
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178
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179 Here are just the tiles that are enclosed by the loop marked with I:
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180
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181 FF7FSF7F7F7F7F7F---7
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182 L|LJ||||||||||||F--J
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183 FL-7LJLJ||||||LJL-77
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184 F--JF--7||LJLJIF7FJ-
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185 L---JF-JLJIIIIFJLJJ7
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186 |F|F-JF---7IIIL7L|7|
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187 |FFJF7L7F-JF7IIL---7
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188 7-L-JL7||F7|L7F-7F7|
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189 L.L7LFJ|||||FJL7||LJ
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190 L7JLJL-JLJLJL--JLJ.L
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191
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192 In this last example, 10 tiles are enclosed by the loop.
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193
19
1e16a25a9553 Strip down the text to just the puzzle, not the fluff
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194 How many tiles are enclosed by the loop?