After saving Christmas five years in a row, you’ve decided to take a vacation at a nice resort on a tropical island. Surely, Christmas will go on without you.
The tropical island has its own currency and is entirely cash-only. The gold coins used there have a little picture of a starfish; the locals just call them stars. None of the currency exchanges seem to have heard of them, but somehow, you’ll need to find fifty of these coins by the time you arrive so you can pay the deposit on your room.
Before you leave, the Elves in accounting just need you to fix your expense report (your puzzle input); apparently, something isn’t quite adding up.
Specifically, they need you to find the two entries that sum to 2020 and then multiply those two numbers together.
library(purrr)
report <- readr::read_lines(here::here("Inputs/input_day01.txt")) %>% as.numeric()Find the two entries that sum to 2020; what do you get if you multiply them together?
diffs <- 2020 - report
prod(intersect(diffs, report))## [1] 1007331
In your expense report, what is the product of the three entries that sum to 2020?
map(diffs, ~ intersect(.x - report, report)) %>%
flatten_dbl() %>%
unique() %>%
prod()## [1] 48914340