2017 Day 16 & Day 17 Complete

2017/day17/problem

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+Advent of Code
+
+--- Day 17: Spinlock ---
+
+   Suddenly, whirling in the distance, you notice what looks like a massive,
+   pixelated hurricane: a deadly spinlock. This spinlock isn't just consuming
+   computing power, but memory, too; vast, digital mountains are being ripped
+   from the ground and consumed by the vortex.
+
+   If you don't move quickly, fixing that printer will be the least of your
+   problems.
+
+   This spinlock's algorithm is simple but efficient, quickly consuming
+   everything in its path. It starts with a circular buffer containing only the
+   value 0, which it marks as the current position. It then steps forward
+   through the circular buffer some number of steps (your puzzle input) before
+   inserting the first new value, 1, after the value it stopped on. The inserted
+   value becomes the current position. Then, it steps forward from there the
+   same number of steps, and wherever it stops, inserts after it the second new
+   value, 2, and uses that as the new current position again.
+
+   It repeats this process of stepping forward, inserting a new value, and using
+   the location of the inserted value as the new current position a total of
+   2017 times, inserting 2017 as its final operation, and ending with a total of
+   2018 values (including 0) in the circular buffer.
+
+   For example, if the spinlock were to step 3 times per insert, the circular
+   buffer would begin to evolve like this (using parentheses to mark the current
+   position after each iteration of the algorithm):
+
+     * (0), the initial state before any insertions.
+     * 0 (1): the spinlock steps forward three times (0, 0, 0), and then inserts
+       the first value, 1, after it. 1 becomes the current position.
+     * 0 (2) 1: the spinlock steps forward three times (0, 1, 0), and then
+       inserts the second value, 2, after it. 2 becomes the current position.
+     * 0  2 (3) 1: the spinlock steps forward three times (1, 0, 2), and then
+       inserts the third value, 3, after it. 3 becomes the current position.
+
+   And so on:
+
+     * 0  2 (4) 3  1
+     * 0 (5) 2  4  3  1
+     * 0  5  2  4  3 (6) 1
+     * 0  5 (7) 2  4  3  6  1
+     * 0  5  7  2  4  3 (8) 6  1
+     * 0 (9) 5  7  2  4  3  8  6  1
+
+   Eventually, after 2017 insertions, the section of the circular buffer near
+   the last insertion looks like this:
+
+ 1512  1134  151 (2017) 638  1513  851
+
+   Perhaps, if you can identify the value that will ultimately be after the last
+   value written (2017), you can short-circuit the spinlock. In this example,
+   that would be 638.
+
+   What is the value after 2017 in your completed circular buffer?
+
+   Your puzzle answer was ________.
+
+--- Part Two ---
+
+   The spinlock does not short-circuit. Instead, it gets more angry. At least,
+   you assume that's what happened; it's spinning significantly faster than it
+   was a moment ago.
+
+   You have good news and bad news.
+
+   The good news is that you have improved calculations for how to stop the
+   spinlock. They indicate that you actually need to identify the value after 0
+   in the current state of the circular buffer.
+
+   The bad news is that while you were determining this, the spinlock has just
+   finished inserting its fifty millionth value (50000000).
+
+   What is the value after 0 the moment 50000000 is inserted?
+
+   Your puzzle answer was _____________.
+
+   Both parts of this puzzle are complete! They provide two gold stars: **
+
+   At this point, you should return to your advent calendar and try another
+   puzzle.
+
+   Your puzzle input was 301.
+
+References
+
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+   . https://en.wikipedia.org/wiki/Spinlock
+   . http://adventofcode.com/2017