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75 lines
2.3 KiB
75 lines
2.3 KiB
--- Day 4: Ceres Search ---
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"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
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As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: XMAS.
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This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of XMAS - you need to find all of them. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:
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..X...
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.SAMX.
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.A..A.
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XMAS.S
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.X....
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The actual word search will be full of letters instead. For example:
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MMMSXXMASM
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MSAMXMSMSA
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AMXSXMAAMM
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MSAMASMSMX
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XMASAMXAMM
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XXAMMXXAMA
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SMSMSASXSS
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SAXAMASAAA
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MAMMMXMMMM
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MXMXAXMASX
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In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:
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....XXMAS.
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.SAMXMS...
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...S..A...
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..A.A.MS.X
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XMASAMX.MM
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X.....XA.A
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S.S.S.S.SS
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.A.A.A.A.A
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..M.M.M.MM
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.X.X.XMASX
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Take a look at the little Elf's word search. How many times does XMAS appear?
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Your puzzle answer was 2493.
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--- Part Two ---
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The Elf looks quizzically at you. Did you misunderstand the assignment?
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Looking for the instructions, you flip over the word search to find that this isn't actually an XMAS puzzle; it's an X-MAS puzzle in which you're supposed to find two MAS in the shape of an X. One way to achieve that is like this:
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M.S
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.A.
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M.S
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Irrelevant characters have again been replaced with . in the above diagram. Within the X, each MAS can be written forwards or backwards.
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Here's the same example from before, but this time all of the X-MASes have been kept instead:
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.M.S......
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..A..MSMS.
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.M.S.MAA..
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..A.ASMSM.
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.M.S.M....
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..........
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S.S.S.S.S.
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.A.A.A.A..
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M.M.M.M.M.
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..........
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In this example, an X-MAS appears 9 times.
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Flip the word search from the instructions back over to the word search side and try again. How many times does an X-MAS appear?
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Your puzzle answer was 1890.
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Both parts of this puzzle are complete! They provide two gold stars: **
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