day25.md

— Day 25: Combo Breaker —

Fleur Kelpin Dec 25, 2020

library(tidyverse)
library(numbers)
input <- read_csv("day25.txt", col_names = "key")
input

## # A tibble: 2 x 1
##        key
##      <dbl>
## 1  5290733
## 2 15231938

Part 1

transform_subject <- function (subject, loop) {
  modpower(subject, loop, 20201227)
}

find_loop_size <- function (key) {
  x <- 1
  loop <- 0
  repeat {
    loop <- loop + 1
    x <- (x * 7) %% 20201227
    if (x == key) {
      return(loop)
    }
  }
}
transform_subject(input$key[[1]], find_loop_size(input$key[[2]]))

## [1] 6198540