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Robert Mion
Robert Mion

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Calorie Counting

#adventofcode #algorithms #javascript #programming

Advent of Code 2022 Day 1

Part 1

  1. Another great lesson in reduce
  2. My algorithm in pseudocode
  3. My algorithm in JavaScript

Another great lesson in reduce

  • From a collection of Elvish calorie counts
  • I want to derive an integer
  • Which represents an amount of calories
  • Associated with the Elf who eats the most calories

Why use reduce()?

  • reduce() is a built-in array method
  • that accumulates one item (can be of any data type)
  • updating that accumulating item after operating on each item in the array
  • tracking the item's value, index, and the source array
  • and returns the accumulated item

I'll take two reduce()ers, please!

  1. A reduce() to iterate through each Elf
  2. A reduce() to iterate through one Elf's itemized calories

My algorithm in pseudocode 

Split the input at each double newline character to create an array of strings representing each Elf For each Elf, accumulate an integer, starting at 0: Split the string at each newline character to create an array of strings representing each food's calorie count For each string, accumulate a number starting at 0: Coerce the string to an integer Increment the accumulating number by the integer Return the accumulated number If this Elf's calorie count is greater than the current largest count Update the accumulating integer to reflect this Elf's calorie count Return the accumulated integer
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My algorithm in JavaScript 

return input .split('\n\n') .reduce((answer, elf) => { const calories = elf .split('\n') .map(Number) .reduce((sum, count) => sum + count) return answer < calories ? calories : answer }, 0)
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Part 2

  1. Make that three reduce()ers, please!
  2. My algorithm in pseudocode
  3. My algorithm in JavaScript

Make that three reduce()ers, please!

  1. A reduce() to iterate through each Elf
  2. A reduce() to iterate through one Elf's itemized calories
  3. A reduce() to sum up the three largest calories

My algorithm in pseudocode 

Split the input at each double newline character to create an array of strings representing each Elf For each Elf, accumulate an array that is initially empty: Split the string at each newline character to create an array of strings representing each food's calorie count For each string, accumulate a number starting at 0: Coerce the string to an integer Increment the accumulating number by the integer Return the accumulated number Add the current Elf's calorie count to the accumulating array Return the accumulated array Sort the array's numbers in descending order Extract only the first three numbers - the largest ones For each number, accumulate a sum Return the sum
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My algorithm in JavaScript 

return input .split('\n\n') .reduce((winner, elf) => { const calories = elf .split('\n') .map(Number) .reduce((sum, count) => sum + count) winner.push(calories) return winner }, []) .sort((a, b) => b - a) .slice(0, 3) .reduce((sum, count) => sum + count)
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I did it!!

  • I solved both parts!
  • I misread the instructions for Part 1. I thought the answer was a particular Elf. But it was just the calorie count, so my code got even simpler!
  • I loved the twist of Part 2, requiring a post-reduce sort and slice!
  • I made a GIF to visualize how my algorithms work!

Never a dull challenge in AoC!

Even the relatively easier ones are great practice!

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