Day 1

Advent of Code: Worked Solutions

Setup

# Libraries
library(tidyverse)

# Read input from file
input <- read_table(
  "../input/day01.txt", 
  col_names = c("x", "y"), 
  show_col_types = FALSE
)

Part 1

Sort each list independently, then sum the distances between each pair of ordered items.

tibble(
  x = sort(input$x), 
  y = sort(input$y),
  dist = abs(y - x)
) |> 
  summarize(total = sum(dist)) |> 
  pull()

[1] 2285373

Part 2

For each item in list x, multiply its value by its number of occurrences in list y, then sum the total.

input |> 
  mutate(
    x_match_count = map_int(x, ~ sum(.x == y)),
    similarity_score = x * x_match_count
  ) |> 
  summarize(total = sum(similarity_score)) |> 
  pull()

[1] 21142653