2022 day 6 init + bash part 1

2022/day06/README.org

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+** --- Day 6: Tuning Trouble ---
+The preparations are finally complete; you and the Elves leave camp on
+foot and begin to make your way toward the /star/ fruit grove.
+
+As you move through the dense undergrowth, one of the Elves gives you a
+handheld /device/. He says that it has many fancy features, but the most
+important one to set up right now is the /communication system/.
+
+However, because he's heard you have [[/2016/day/6][significant]]
+[[/2016/day/25][experience]] [[/2019/day/7][dealing]]
+[[/2019/day/9][with]] [[/2019/day/16][signal-based]]
+[[/2021/day/25][systems]], he convinced the other Elves that it would be
+okay to give you their one malfunctioning device - surely you'll have no
+problem fixing it.
+
+As if inspired by comedic timing, the device emits a few colorful
+sparks.
+
+To be able to communicate with the Elves, the device needs to /lock on
+to their signal/. The signal is a series of seemingly-random characters
+that the device receives one at a time.
+
+To fix the communication system, you need to add a subroutine to the
+device that detects a /start-of-packet marker/ in the datastream. In the
+protocol being used by the Elves, the start of a packet is indicated by
+a sequence of /four characters that are all different/.
+
+The device will send your subroutine a datastream buffer (your puzzle
+input); your subroutine needs to identify the first position where the
+four most recently received characters were all different. Specifically,
+it needs to report the number of characters from the beginning of the
+buffer to the end of the first such four-character marker.
+
+For example, suppose you receive the following datastream buffer:
+
+#+begin_example
+mjqjpqmgbljsphdztnvjfqwrcgsmlb
+#+end_example
+
+After the first three characters (=mjq=) have been received, there
+haven't been enough characters received yet to find the marker. The
+first time a marker could occur is after the fourth character is
+received, making the most recent four characters =mjqj=. Because =j= is
+repeated, this isn't a marker.
+
+The first time a marker appears is after the /seventh/ character
+arrives. Once it does, the last four characters received are =jpqm=,
+which are all different. In this case, your subroutine should report the
+value =7=, because the first start-of-packet marker is complete after 7
+characters have been processed.
+
+Here are a few more examples:
+
+- =bvwbjplbgvbhsrlpgdmjqwftvncz=: first marker after character =5=
+- =nppdvjthqldpwncqszvftbrmjlhg=: first marker after character =6=
+- =nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg=: first marker after character =10=
+- =zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw=: first marker after character =11=
+
+/How many characters need to be processed before the first
+start-of-packet marker is detected?/
+
+Your puzzle answer was =1658=.
+
+The first half of this puzzle is complete! It provides one gold star: *
+
+** --- Part Two ---
+Your device's communication system is correctly detecting packets, but
+still isn't working. It looks like it also needs to look for /messages/.
+
+A /start-of-message marker/ is just like a start-of-packet marker,
+except it consists of /14 distinct characters/ rather than 4.
+
+Here are the first positions of start-of-message markers for all of the
+above examples:
+
+- =mjqjpqmgbljsphdztnvjfqwrcgsmlb=: first marker after character =19=
+- =bvwbjplbgvbhsrlpgdmjqwftvncz=: first marker after character =23=
+- =nppdvjthqldpwncqszvftbrmjlhg=: first marker after character =23=
+- =nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg=: first marker after character =29=
+- =zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw=: first marker after character =26=
+
+/How many characters need to be processed before the first
+start-of-message marker is detected?/
+
+Answer:
+
+Although it hasn't changed, you can still [[file:6/input][get your
+puzzle input]].
+
+You can also [Shareon
+[[https://twitter.com/intent/tweet?text=I%27ve+completed+Part+One+of+%22Tuning+Trouble%22+%2D+Day+6+%2D+Advent+of+Code+2022&url=https%3A%2F%2Fadventofcode%2Ecom%2F2022%2Fday%2F6&related=ericwastl&hashtags=AdventOfCode][Twitter]]
+[[javascript:void(0);][Mastodon]]] this puzzle.