day 7

Author: mflinn-broad

src/days/day7.rs

@@ -0,0 +1,71 @@
+use crate::util;
+
+pub fn run() {
+    let raw_input = util::read_input("inputs/day7.txt").unwrap();
+    let input = process(&raw_input);
+
+    println!("Part 1: {}", part_1(&mut input.clone()));
+    println!("Part 2: {}", part_2(&input));
+}
+
+fn process(input: &str) -> Vec<usize> {
+    input
+        .trim()
+        .split(',')
+        .map(|pos| pos.parse().unwrap())
+        .collect()
+}
+
+fn part_1(input: &mut Vec<usize>) -> usize {
+    input.sort();
+
+    let median = input[(input.len() / 2) + (input.len() % 2)];
+    cost_at(median, &input)
+}
+
+fn part_2(input: &Vec<usize>) -> usize {
+    let mean: usize = input.iter().sum::<usize>() / input.len();
+    (mean - 5..mean + 5)
+        .map(|pos| cost_at_v2(pos, input))
+        .min()
+        .unwrap()
+}
+
+fn cost_at(pos: usize, crabs: &Vec<usize>) -> usize {
+    crabs.iter().map(|crab_pos| pos.abs_diff(*crab_pos)).sum()
+}
+
+fn cost_at_v2(pos: usize, crabs: &Vec<usize>) -> usize {
+    crabs
+        .iter()
+        .map(|crab_pos| {
+            let abs_dist = pos.abs_diff(*crab_pos);
+            abs_dist * (1 + abs_dist) / 2
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    extern crate test;
+    use test::Bencher;
+
+    #[bench]
+    fn bench_part_1(b: &mut Bencher) {
+        let raw_input = util::read_input("inputs/day7.txt").unwrap();
+        b.iter(|| {
+            let mut input = process(&raw_input);
+            part_1(&mut input);
+        });
+    }
+
+    #[bench]
+    fn bench_part_2(b: &mut Bencher) {
+        let raw_input = util::read_input("inputs/day7.txt").unwrap();
+        b.iter(|| {
+            let input = process(&raw_input);
+            part_2(&input);
+        });
+    }
+}

src/days/mod.rs

@@ -4,3 +4,4 @@ pub mod day3;
 pub mod day4;
 pub mod day5;
 pub mod day6;
+pub mod day7;

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(drain_filter, test)]
+#![feature(drain_filter, test, int_abs_diff)]
 
 pub mod days;
 mod util;

src/main.rs

@@ -13,4 +13,6 @@ fn main() {
     day5::run();
     println!("Day 6 --------");
     day6::run();
+    println!("Day 7 --------");
+    day7::run();
 }