Day 1

Advent of Code: Worked Solutions

Setup

Import libraries:

library(tidyverse)

Read text input from file into a data frame:

input <- read_table("../input/day01.txt", col_names = c("x", "y"))

Part 1

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

sum(abs(sort(input$x) - sort(input$y)))

Part 2

For each item in list x, multiply its value by its number of occurrences in list y, then sum the total. Since an x value occurring 0 times in list y doesn’t contribute to the total, we can just filter y to the values also in x and sum the result:

sum(keep(input$y, \(y) y %in% input$x))