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--- Day 4: Ceres Search --- "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! 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. 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 .: ..X... .SAMX. .A..A. XMAS.S .X.... The actual word search will be full of letters instead. For example: MMMSXXMASM MSAMXMSMSA AMXSXMAAMM MSAMASMSMX XMASAMXAMM XXAMMXXAMA SMSMSASXSS SAXAMASAAA MAMMMXMMMM MXMXAXMASX 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 .: ....XXMAS. .SAMXMS... ...S..A... ..A.A.MS.X XMASAMX.MM X.....XA.A S.S.S.S.SS .A.A.A.A.A ..M.M.M.MM .X.X.XMASX Take a look at the little Elf's word search. How many times does XMAS appear? --- Part Two --- The Elf looks quizzically at you. Did you misunderstand the assignment? 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: M.S .A. M.S Irrelevant characters have again been replaced with . in the above diagram. Within the X, each MAS can be written forwards or backwards. Here's the same example from before, but this time all of the X-MASes have been kept instead: .M.S...... ..A..MSMS. .M.S.MAA.. ..A.ASMSM. .M.S.M.... .......... S.S.S.S.S. .A.A.A.A.. M.M.M.M.M. .......... In this example, an X-MAS appears 9 times. 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? |