Day 10

Data

Input is a series of CPU instructions.

input_file <- here("DATA", "2022", "input_day_10.txt")

cat(system(paste0("head ", input_file), intern = TRUE), sep = "\n")

noop
noop
addx 5
addx 29
addx -28
addx 5
addx -1
noop
noop
addx 5

all_instructions <- scan(
  input_file,
  what = "character",
  sep = "\n"
)

There are two types of instructions:

• noop - lasts one cycle and doesn’t do anything;
• addx V - lasts two cycles and after two cycles, the X register has increased by V (can be also negative)

I will need to follow the cycles and the X register.

Functions

increase_cycle <- function(){
  cycle <<- cycle + 1
}

copy_last_reg <- function(){
  register[cycle + 1] <<- register[cycle]
}

add_to_reg <- function(V){
  register[cycle + 1] <<- register[cycle] + V
}

Run cycles

I need to know of only 220 cycles.

register <- rep(NA, 240)
# register starts with 1
register[1] <- 1
head(register)

[1]  1 NA NA NA NA NA

I will need to start from cycle 1 instead of 0.

start_cycle <- 1
cycle <- start_cycle

idx <- 1
copy_last_reg()
while(idx <= length(all_instructions)){
  instruction <- all_instructions[idx]
  
  if(instruction == "noop"){
    increase_cycle()
    copy_last_reg()
  } else {
    V <- as.numeric(word(instruction, 2))
    
    increase_cycle()
    copy_last_reg()
    increase_cycle()
    add_to_reg(V)
  }
  idx <<- idx + 1
}

Compute total strength

The signal strength is equal to the multiplication of the X register value and cycle number. We focus on cycles: 20, 60, 100, 140, 180, and 220.

chosen_cycles <- c(20, 60, 100, 140, 180, 220)
sum_signal_strengths <- sum(chosen_cycles*register[chosen_cycles + 1])

The sum of chosen signal strengths is 1.492^{4}! 🥳