05: A Maze of Twisty Trampolines, All Alike

library(mistlecode)

x2 <- 
  readLines("input.txt") |>
  as.integer()

Part 1

I tried recursion first, had a bit of trouble, then got C stack errors. Back to while loops we go…

x <- x2
pos <- 1
inc <- 0
while(pos >= 1 & pos <= length(x)) {
  x[pos] <- x[pos] + 1
  pos <- pos + x[pos] - 1
  inc <- inc + 1
}
inc

[1] 376976

Part 2

For some reason I struggled with getting the logic in the right order, but a poor night’s sleep does wonders :|

x <- x2
pos <- 1
inc <- 0
while(pos >= 1 & pos <= length(x)) {
  jmp <- x[pos]
  x[pos] <- if(x[pos] >= 3) x[pos] - 1 else x[pos] + 1
  inc <- inc + 1
  pos <- pos + jmp
}
inc

[1] 29227751