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Advent of Code 2015 Day 2

Day 2: I Was Told There Would Be No Math

https://adventofcode.com/2015/day/2

The elves would like to order the exact amount of wrapping paper they need to wrap all presents.

Each present is a perfectly rectangular box.

Today’s input is a list with the dimensions of each gift.

An example input looks like this:

input.txt
29x13x26
11x11x14
27x2x5

Each line has the form of LxWxH.

For the first present in the list above:

  • length: 29
  • width: 13
  • height: 26

Those numbers are unitless. Let’s say Santa uses the imperial system to measure presents. They’re measured in feet.

Part 1

The required amount of wrapping paper for one present:

  • Enough to cover all sides
  • Some extra: the area of the smallest side

The question asks how many square foot of wrapping paper is needed to wrap all presents.

Main code for part 1

day_02.rs
pub fn part_1(input: &str) -> i32 {
    input
        .lines()
        .map(|line| {
            let mut nums = line.split('x').map(|s| s.parse::<i32>().unwrap());
            // dimensions
            let l = nums.next().unwrap();
            let w = nums.next().unwrap();
            let h = nums.next().unwrap();
            // sides
            let lw = l * w;
            let wh = w * h;
            let lh = l * h;
            let smallest = lw.min(wh).min(lh);


            2 * lw + 2 * wh + 2 * lh + smallest
        })
        .sum()
}

Part 2

The elves need to order ribbon too.

The required amount of ribbon for one present:

  • Enough to wrap around the smallest perimeter
  • Some extra for a bow: the cubic feet of volume for the present

The question asks how many feet of ribbon is needed to wrap all presents with a bow.

A minor change from part 1: I sorted the dimensions to be able to use the 2 smallest ones.

Main code for part 2

day_01.rs
pub fn part_2(input: &str) -> i32 {
    input
    .lines()
    .map(|line| {
        let mut nums = line.split('x').map(|s| s.parse::<i32>().unwrap()).sorted_unstable();
        // dimensions from small to big
        let dim1 = nums.next().unwrap();
        let dim2 = nums.next().unwrap();
        let dim3 = nums.next().unwrap();


        2 * dim1 + 2 * dim2 + dim1 * dim2 * dim3
    })
    .sum()
}

Final code

day_02.rs
use itertools::Itertools;


pub fn part_1(input: &str) -> i32 {
    input
        .lines()
        .map(|line| {
            let mut nums = line.split('x').map(|s| s.parse::<i32>().unwrap());
            // dimensions
            let l = nums.next().unwrap();
            let w = nums.next().unwrap();
            let h = nums.next().unwrap();
            // sides
            let lw = l * w;
            let wh = w * h;
            let lh = l * h;
            let smallest = lw.min(wh).min(lh);


            2 * lw + 2 * wh + 2 * lh + smallest
        })
        .sum()
}


pub fn part_2(input: &str) -> i32 {
    input
    .lines()
    .map(|line| {
        let mut nums = line.split('x').map(|s| s.parse::<i32>().unwrap()).sorted_unstable();
        // dimensions from small to big
        let dim1 = nums.next().unwrap();
        let dim2 = nums.next().unwrap();
        let dim3 = nums.next().unwrap();


        2 * dim1 + 2 * dim2 + dim1 * dim2 * dim3
    })
    .sum()
}