Advent of Code Day 1

Here is my solution to Advent of Code, Day 1:

(def input (slurp "day1.txt"))

(def elf-totals 
  (->> (clojure.string/split input #"\n\n")
       (map (fn [elf-row] (clojure.string/split elf-row #"\n")))
       (map (fn [elf-row] 
              (map (fn [calorie-value] (Integer/parseInt calorie-value)) elf-row)))
       (into []) 
       (map (fn [elf-row] (reduce + elf-row)))
       (sort (fn [x y] (> x y)))
       (take 3)))

(def answer
  (list (reduce + elf-totals) (first elf-totals)))

It is an overuse of maps and reduces, but let’s go through it step-by-step.

I start by slurping in the input day1.txt, which is a collection of newline delimited numbers representing multiple elves. Then, I push that input through a series of transforms with the thread-last macro ->>.

Splitting the input by a double newline gives me each elf in it’s own sequence. The elves are delimited by blank lines (an additional newline character). Then I split each row by the newline character to give me every number in a row.

Next, I run Java’s Integer/parseInt to get the numerical values of each number in an elf row, then I coerce those values into a vector using into.

After, I reduce the elf rows by summing each one, sort the rows in descending order, and take 3 elements from the front of the sequence. My answer is then the first of the top 3 elf totals, and the sum of the top 3 elf totals.

Looking forward to the rest of the puzzles!


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