76 lines
3.4 KiB
Org Mode
76 lines
3.4 KiB
Org Mode
** --- Day 1: The Tyranny of the Rocket Equation ---
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Santa has become stranded at the edge of the Solar System while
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delivering presents to other planets! To accurately calculate his
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position in space, safely align his warp drive, and return to Earth in
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time to save Christmas, he needs you to bring him measurements from
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/fifty stars/.
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Collect stars by solving puzzles. Two puzzles will be made available on
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each day in the Advent calendar; the second puzzle is unlocked when you
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complete the first. Each puzzle grants /one star/. Good luck!
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The Elves quickly load you into a spacecraft and prepare to launch.
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At the first Go / No Go poll, every Elf is Go until the Fuel
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Counter-Upper. They haven't determined the amount of fuel required yet.
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Fuel required to launch a given /module/ is based on its /mass/.
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Specifically, to find the fuel required for a module, take its mass,
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divide by three, round down, and subtract 2.
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For example:
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- For a mass of =12=, divide by 3 and round down to get =4=, then
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subtract 2 to get =2=.
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- For a mass of =14=, dividing by 3 and rounding down still yields =4=,
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so the fuel required is also =2=.
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- For a mass of =1969=, the fuel required is =654=.
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- For a mass of =100756=, the fuel required is =33583=.
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The Fuel Counter-Upper needs to know the total fuel requirement. To find
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it, individually calculate the fuel needed for the mass of each module
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(your puzzle input), then add together all the fuel values.
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/What is the sum of the fuel requirements/ for all of the modules on
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your spacecraft?
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Your puzzle answer was =3318604=.
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** --- Part Two ---
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During the second Go / No Go poll, the Elf in charge of the Rocket
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Equation Double-Checker stops the launch sequence. Apparently, you
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forgot to include additional fuel for the fuel you just added.
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Fuel itself requires fuel just like a module - take its mass, divide by
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three, round down, and subtract 2. However, that fuel /also/ requires
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fuel, and /that/ fuel requires fuel, and so on. Any mass that would
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require /negative fuel/ should instead be treated as if it requires
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/zero fuel/; the remaining mass, if any, is instead handled by /wishing
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really hard/, which has no mass and is outside the scope of this
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calculation.
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So, for each module mass, calculate its fuel and add it to the total.
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Then, treat the fuel amount you just calculated as the input mass and
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repeat the process, continuing until a fuel requirement is zero or
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negative. For example:
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- A module of mass =14= requires =2= fuel. This fuel requires no further
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fuel (2 divided by 3 and rounded down is =0=, which would call for a
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negative fuel), so the total fuel required is still just =2=.
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- At first, a module of mass =1969= requires =654= fuel. Then, this fuel
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requires =216= more fuel (=654 / 3 - 2=). =216= then requires =70=
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more fuel, which requires =21= fuel, which requires =5= fuel, which
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requires no further fuel. So, the total fuel required for a module of
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mass =1969= is =654 + 216 + 70 + 21 + 5 = 966=.
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- The fuel required by a module of mass =100756= and its fuel is:
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=33583 + 11192 + 3728 + 1240 + 411 + 135 + 43 + 12 + 2 = 50346=.
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/What is the sum of the fuel requirements/ for all of the modules on
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your spacecraft when also taking into account the mass of the added
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fuel? (Calculate the fuel requirements for each module separately, then
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add them all up at the end.)
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Your puzzle answer was =4975039=.
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Both parts of this puzzle are complete! They provide two gold stars: **
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