Day 19 Complete

2016/day19/problem

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+Advent of Code
+
+--- Day 19: An Elephant Named Joseph ---
+
+   The Elves contact you over a highly secure emergency channel. Back at the
+   North Pole, the Elves are busy misunderstanding White Elephant parties.
+
+   Each Elf brings a present. They all sit in a circle, numbered starting
+   with position 1. Then, starting with the first Elf, they take turns
+   stealing all the presents from the Elf to their left. An Elf with no
+   presents is removed from the circle and does not take turns.
+
+   For example, with five Elves (numbered 1 to 5):
+
+   1
+ 5   2
+  4 3
+
+     • Elf 1 takes Elf 2's present.
+     • Elf 2 has no presents and is skipped.
+     • Elf 3 takes Elf 4's present.
+     • Elf 4 has no presents and is also skipped.
+     • Elf 5 takes Elf 1's two presents.
+     • Neither Elf 1 nor Elf 2 have any presents, so both are skipped.
+     • Elf 3 takes Elf 5's three presents.
+
+   So, with five Elves, the Elf that sits starting in position 3 gets all the
+   presents.
+
+   With the number of Elves given in your puzzle input, which Elf gets all
+   the presents?
+
+   Your puzzle input was 3014387.
+
+   Your puzzle answer was __________.
+
+--- Part Two ---
+
+   Realizing the folly of their present-exchange rules, the Elves agree to
+   instead steal presents from the Elf directly across the circle. If two
+   Elves are across the circle, the one on the left (from the perspective of
+   the stealer) is stolen from. The other rules remain unchanged: Elves with
+   no presents are removed from the circle entirely, and the other elves move
+   in slightly to keep the circle evenly spaced.
+
+   For example, with five Elves (again numbered 1 to 5):
+
+     • The Elves sit in a circle; Elf 1 goes first:
+
+   1
+ 5   2
+  4 3
+
+     • Elves 3 and 4 are across the circle; Elf 3's present is stolen, being
+       the one to the left. Elf 3 leaves the circle, and the rest of the
+       Elves move in:
+
+   1           1
+ 5   2  -->  5   2
+  4 -          4
+
+     • Elf 2 steals from the Elf directly across the circle, Elf 5:
+
+   1         1
+ -   2  -->     2
+   4         4
+
+     • Next is Elf 4 who, choosing between Elves 1 and 2, steals from Elf 1:
+
+  -          2
+     2  -->
+  4          4
+
+     • Finally, Elf 2 steals from Elf 4:
+
+  2
+     -->  2
+  -
+
+   So, with five Elves, the Elf that sits starting in position 2 gets all the
+   presents.
+
+   With the number of Elves given in your puzzle input, which Elf now gets
+   all the presents?
+
+   Your puzzle input was 3014387.
+
+   Your puzzle answer was __________.
+
+References
+
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