2019-12-01

# Day 01: The Tyranny of the Rocket Equation

Description:
--- Day 1: The Tyranny of the Rocket Equation ---

Santa has become stranded at the edge of the Solar System while delivering presents to other planets! To accurately calculate his position in space, safely align his warp drive, and return to Earth in time to save Christmas, he needs you to bring him measurements from fifty stars.

Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck!

The Elves quickly load you into a spacecraft and prepare to launch.

At the first Go / No Go poll, every Elf is Go until the Fuel Counter-Upper. They haven't determined the amount of fuel required yet.

Fuel required to launch a given module is based on its mass. Specifically, to find the fuel required for a module, take its mass, divide by three, round down, and subtract 2.

For example:

For a mass of 12, divide by 3 and round down to get 4, then subtract 2 to get 2.
For a mass of 14, dividing by 3 and rounding down still yields 4, so the fuel required is also 2.
For a mass of 1969, the fuel required is 654.
For a mass of 100756, the fuel required is 33583.

The Fuel Counter-Upper needs to know the total fuel requirement. To find it, individually calculate the fuel needed for the mass of each module (your puzzle input), then add together all the fuel values.

What is the sum of the fuel requirements for all of the modules on your spacecraft?

--- Part Two ---

During the second Go / No Go poll, the Elf in charge of the Rocket Equation Double-Checker stops the launch sequence. Apparently, you forgot to include additional fuel for the fuel you just added.

Fuel itself requires fuel just like a module - take its mass, divide by three, round down, and subtract 2. However, that fuel also requires fuel, and that fuel requires fuel, and so on. Any mass that would require negative fuel should instead be treated as if it requires zero fuel; the remaining mass, if any, is instead handled by wishing really hard, which has no mass and is outside the scope of this calculation.

So, for each module mass, calculate its fuel and add it to the total. Then, treat the fuel amount you just calculated as the input mass and repeat the process, continuing until a fuel requirement is zero or negative. For example:

A module of mass 14 requires 2 fuel. This fuel requires no further fuel (2 divided by 3 and rounded down is 0, which would call for a negative fuel), so the total fuel required is still just 2.
At first, a module of mass 1969 requires 654 fuel. Then, this fuel requires 216 more fuel (654 / 3 - 2). 216 then requires 70 more fuel, which requires 21 fuel, which requires 5 fuel, which requires no further fuel. So, the total fuel required for a module of mass 1969 is 654 + 216 + 70 + 21 + 5 = 966.
The fuel required by a module of mass 100756 and its fuel is: 33583 + 11192 + 3728 + 1240 + 411 + 135 + 43 + 12 + 2 = 50346.

What is the sum of the fuel requirements for all of the modules on your spacecraft when also taking into account the mass of the added fuel? (Calculate the fuel requirements for each module separately, then add them all up at the end.)

Input:
63455
147371
83071
57460
74392
145303
130181
53102
120073
93111
144471
105327
116466
67222
122845
146097
92014
114428
96796
131140
101481
87953
101415
75739
64263
94257
140426
62387
84464
104547
103581
89121
123301
64993
143555
55246
120986
67596
146173
149707
60285
83517
73782
103464
140506
78400
140672
141638
84470
116879
100701
63976
135748
65021
120086
147249
55441
135315
147426
93676
91384
110918
123368
102430
144807
82761
134357
62990
85171
134886
69166
119744
80648
96752
89379
136178
95175
124306
51990
57564
111347
79317
95357
85765
137827
105014
110742
105014
149330
78437
107908
139044
143304
90614
52119
147113
119815
125634
104335
138295

Part 1:
``````namespace AdventOfCode2019_01_1
{
const DAY     = 1;
const PROBLEM = 1;

export async function run()
{
if (input == null) return;

const fuel = input
.split(new RegExp('\r?\n'))
.filter(p => p.trim().length > 0)
.map(p => parseInt(p))
.map(p => Math.floor(p/3) - 2)
.reduce((a,b) => a+b);

}
}
``````
Result: 3464458

Part 2:
``````namespace AdventOfCode2019_01_2
{
const DAY     = 1;
const PROBLEM = 2;

export async function run()
{
if (input == null) return;

const fuel = input
.split(new RegExp('\r?\n'))
.filter(p => p.trim().length > 0)
.map(p => parseInt(p))
.map(mass =>
{
let fuel = Math.floor(mass / 3) - 2;
let lastfuel = fuel;
for (; ; )
{
let newfuel = Math.floor(lastfuel / 3) - 2;
if (newfuel <= 0) break;
fuel += newfuel;
lastfuel = newfuel;
}
return fuel;
})
.reduce((a,b) => a+b);