diff --git a/2017/09/solution.py b/2017/09/solution.py index 78d8286..c0e8d1a 100644 --- a/2017/09/solution.py +++ b/2017/09/solution.py @@ -29,7 +29,7 @@ if part == 1: ######################################### # # -# not working Part 2 # +# Part 2 # # # ######################################### if part == 2: diff --git a/2017/10/10.md b/2017/10/10.md new file mode 100644 index 0000000..e677260 --- /dev/null +++ b/2017/10/10.md @@ -0,0 +1,169 @@ +## \-\-- Day 10: Knot Hash \-\-- + +You come across some programs that are trying to implement a software +emulation of a hash based on knot-tying. The hash these programs are +implementing isn\'t very strong, but you decide to help them anyway. You +make a mental note to remind the Elves later not to [invent their own +cryptographic functions]{title="NEW CRYPTOSYSTEM WHO DIS"}. + +This hash function simulates tying a knot in a circle of string with 256 +marks on it. Based on the input to be hashed, the function repeatedly +selects a span of string, brings the ends together, and gives the span a +half-twist to reverse the order of the marks within it. After doing this +many times, the order of the marks is used to build the resulting hash. + + 4--5 pinch 4 5 4 1 + / \ 5,0,1 / \/ \ twist / \ / \ + 3 0 --> 3 0 --> 3 X 0 + \ / \ /\ / \ / \ / + 2--1 2 1 2 5 + +To achieve this, begin with a *list* of numbers from `0` to `255`, a +*current position* which begins at `0` (the first element in the list), +a *skip size* (which starts at `0`), and a sequence of *lengths* (your +puzzle input). Then, for each length: + +- *Reverse* the order of that *length* of elements in the *list*, + starting with the element at the *current position*. +- *Move* the *current position* forward by that *length* plus the + *skip size*. +- *Increase* the *skip size* by one. + +The *list* is circular; if the *current position* and the *length* try +to reverse elements beyond the end of the list, the operation reverses +using as many extra elements as it needs from the front of the list. If +the *current position* moves past the end of the list, it wraps around +to the front. *Lengths* larger than the size of the *list* are invalid. + +Here\'s an example using a smaller list: + +Suppose we instead only had a circular list containing five elements, +`0, 1, 2, 3, 4`, and were given input lengths of `3, 4, 1, 5`. + +- The list begins as `[0] 1 2 3 4` (where square brackets indicate the + *current position*). +- The first length, `3`, selects `([0] 1 2) 3 4` (where parentheses + indicate the sublist to be reversed). +- After reversing that section (`0 1 2` into `2 1 0`), we get + `([2] 1 0) 3 4`. +- Then, the *current position* moves forward by the *length*, `3`, + plus the *skip size*, 0: `2 1 0 [3] 4`. Finally, the *skip size* + increases to `1`. + +```{=html} + +``` +- The second length, `4`, selects a section which wraps: + `2 1) 0 ([3] 4`. +- The sublist `3 4 2 1` is reversed to form `1 2 4 3`: + `4 3) 0 ([1] 2`. +- The *current position* moves forward by the *length* plus the *skip + size*, a total of `5`, causing it not to move because it wraps + around: `4 3 0 [1] 2`. The *skip size* increases to `2`. + +```{=html} + +``` +- The third length, `1`, selects a sublist of a single element, and so + reversing it has no effect. +- The *current position* moves forward by the *length* (`1`) plus the + *skip size* (`2`): `4 [3] 0 1 2`. The *skip size* increases to `3`. + +```{=html} + +``` +- The fourth length, `5`, selects every element starting with the + second: `4) ([3] 0 1 2`. Reversing this sublist (`3 0 1 2 4` into + `4 2 1 0 3`) produces: `3) ([4] 2 1 0`. +- Finally, the *current position* moves forward by `8`: `3 4 2 1 [0]`. + The *skip size* increases to `4`. + +In this example, the first two numbers in the list end up being `3` and +`4`; to check the process, you can multiply them together to produce +`12`. + +However, you should instead use the standard list size of `256` (with +values `0` to `255`) and the sequence of *lengths* in your puzzle input. +Once this process is complete, *what is the result of multiplying the +first two numbers in the list*? + +Your puzzle answer was `19591`. + +The first half of this puzzle is complete! It provides one gold star: \* + +## \-\-- Part Two \-\-- {#part2} + +The logic you\'ve constructed forms a single *round* of the *Knot Hash* +algorithm; running the full thing requires many of these rounds. Some +input and output processing is also required. + +First, from now on, your input should be taken not as a list of numbers, +but as a string of bytes instead. Unless otherwise specified, convert +characters to bytes using their [ASCII +codes](https://en.wikipedia.org/wiki/ASCII#Printable_characters). This +will allow you to handle arbitrary ASCII strings, and it also ensures +that your input lengths are never larger than `255`. For example, if you +are given `1,2,3`, you should convert it to the ASCII codes for each +character: `49,44,50,44,51`. + +Once you have determined the sequence of lengths to use, add the +following lengths to the end of the sequence: `17, 31, 73, 47, 23`. For +example, if you are given `1,2,3`, your final sequence of lengths should +be `49,44,50,44,51,17,31,73,47,23` (the ASCII codes from the input +string combined with the standard length suffix values). + +Second, instead of merely running one *round* like you did above, run a +total of `64` rounds, using the same *length* sequence in each round. +The *current position* and *skip size* should be preserved between +rounds. For example, if the previous example was your first round, you +would start your second round with the same *length* sequence +(`3, 4, 1, 5, 17, 31, 73, 47, 23`, now assuming they came from ASCII +codes and include the suffix), but start with the previous round\'s +*current position* (`4`) and *skip size* (`4`). + +Once the rounds are complete, you will be left with the numbers from `0` +to `255` in some order, called the *sparse hash*. Your next task is to +reduce these to a list of only `16` numbers called the *dense hash*. To +do this, use numeric bitwise +[XOR](https://en.wikipedia.org/wiki/Bitwise_operation#XOR) to combine +each consecutive block of `16` numbers in the sparse hash (there are +`16` such blocks in a list of `256` numbers). So, the first element in +the dense hash is the first sixteen elements of the sparse hash XOR\'d +together, the second element in the dense hash is the second sixteen +elements of the sparse hash XOR\'d together, etc. + +For example, if the first sixteen elements of your sparse hash are as +shown below, and the XOR operator is `^`, you would calculate the first +output number like this: + + 65 ^ 27 ^ 9 ^ 1 ^ 4 ^ 3 ^ 40 ^ 50 ^ 91 ^ 7 ^ 6 ^ 0 ^ 2 ^ 5 ^ 68 ^ 22 = 64 + +Perform this operation on each of the sixteen blocks of sixteen numbers +in your sparse hash to determine the sixteen numbers in your dense hash. + +Finally, the standard way to represent a Knot Hash is as a single +[hexadecimal](https://en.wikipedia.org/wiki/Hexadecimal) string; the +final output is the dense hash in hexadecimal notation. Because each +number in your dense hash will be between `0` and `255` (inclusive), +always represent each number as two hexadecimal digits (including a +leading zero as necessary). So, if your first three numbers are +`64, 7, 255`, they correspond to the hexadecimal numbers `40, 07, ff`, +and so the first six characters of the hash would be `4007ff`. Because +every Knot Hash is sixteen such numbers, the hexadecimal representation +is always `32` hexadecimal digits (`0`-`f`) long. + +Here are some example hashes: + +- The empty string becomes `a2582a3a0e66e6e86e3812dcb672a272`. +- `AoC 2017` becomes `33efeb34ea91902bb2f59c9920caa6cd`. +- `1,2,3` becomes `3efbe78a8d82f29979031a4aa0b16a9d`. +- `1,2,4` becomes `63960835bcdc130f0b66d7ff4f6a5a8e`. + +Treating your puzzle input as a string of ASCII characters, *what is the +Knot Hash of your puzzle input?* Ignore any leading or trailing +whitespace you might encounter. + +Answer: + +Although it hasn\'t changed, you can still [get your puzzle +input](10/input). diff --git a/2017/10/solution.py b/2017/10/solution.py new file mode 100644 index 0000000..fc9b799 --- /dev/null +++ b/2017/10/solution.py @@ -0,0 +1,49 @@ +#!/bin/python3 +import sys,re +from pprint import pprint + +input_f = 'input' + +def list2int(x): + return list(map(int, x)) + +part = 1 +######################################### +# # +# Part 1 # +# # +######################################### + +if part == 1: + + size = 256 + lengths = [] + skip = 0 + numbers = [] + pos = 0 + for i in range(0,size): + numbers.append(i) + + with open(input_f) as file: + for line in file: + lengths = list2int(line.rsplit()[0].split(',')) + + for ldx, length in enumerate(lengths): + sub = [numbers[(pos + i) % len(numbers)] for i in range(length)] + rev = sub[::-1] + + for i in range(length): + numbers[(pos + i) % len(numbers)] = rev[i] + + pos += (length+skip) + pos = pos % len(numbers) + skip += 1 + print(numbers[0]*numbers[1]) + +######################################### +# # +# Part 2 # +# # +######################################### +if part == 2: + exit()