2022-20: Grove Positioning System

This looks too good to be true!

library(mistlecode)

To install `mistlecode` yourself, run `devtools::install_github('guslipkin/mistlecode')`.

 Also loading:  cipheR data.table dplyr purrr slider stringr tidyverse

options(scipen = 999)

dt <- 
  readLines("input.txt") |>
  as.numeric()

Part 1

Pretty straightforward, all things considered. Getting vectors to wrap is always a pain. I also missed the bit about the numbers being after zero, but a quick which took care of that.

pos <- 1:length(dt)

shift <- function(pos, x, shift) {
  if (x == 0) { return(pos) }
  p <- which(pos == x)
  pos <- pos[-p]
  after <- (p - 1 + shift) %% length(pos)
  after <- ifelse(after == 0, length(pos), after)
  append(pos, x, after = after)
}

for(i in 1:length(dt)) { pos <- shift(pos, i, dt[i]) }

get_sum <- function(dt, pos) {
  zero <- which(dt[pos] == 0)
  sapply(c(1e3, 2e3, 3e3), \(x) {
    x <- (x + zero) %% length(pos)
    x <- ifelse(x == 0, length(pos), x)
    dt[pos[x]]
  }) |>
    sum()
}

get_sum(dt, pos)

[1] 4151

Part 2

Basically the same as Part 1. I was blessed with no integer overflows so that’s nice. Just multiply the vector by a constant, nest the for loop, then get the sum using the function from Part 1.

key <- 811589153
dt2 <- dt * key
pos2 <- 1:length(dt)

for(j in 1:10) {
  for (i in 1:length(dt2)) { pos2 <- shift(pos2, i, dt2[i]) }
}

get_sum(dt2, pos2)

[1] 7848878698663