From 6d72191e2ce5d423ca03c894d2dad1d3061bd4f3 Mon Sep 17 00:00:00 2001
From: Justin Wernick <justin@worthe-it.co.za>
Date: Tue, 19 Apr 2022 20:27:29 +0200
Subject: Refile for merging repos

---
 2021/src/bin/day_7.rs | 88 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 2021/src/bin/day_7.rs

(limited to '2021/src/bin/day_7.rs')

diff --git a/2021/src/bin/day_7.rs b/2021/src/bin/day_7.rs
new file mode 100644
index 0000000..b568e07
--- /dev/null
+++ b/2021/src/bin/day_7.rs
@@ -0,0 +1,88 @@
+use nom::{
+    bytes::complete::tag, character::complete::u64 as nom_u64, combinator::map,
+    multi::separated_list1, IResult,
+};
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_7.txt")?;
+    let crabs = parse_swarm(&input).unwrap().1;
+    dbg!(crabs.linear_min_fuel_sum());
+    dbg!(crabs.exponential_min_fuel_sum());
+    Ok(())
+}
+
+#[derive(
+    Default, Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, derive_more::Add, derive_more::Sum,
+)]
+struct Fuel(u64);
+
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+struct CrabPosition(u64);
+
+impl CrabPosition {
+    fn linear_fuel(&self, rhs: &Self) -> Fuel {
+        if self > rhs {
+            Fuel(self.0 - rhs.0)
+        } else {
+            Fuel(rhs.0 - self.0)
+        }
+    }
+
+    fn exponential_fuel(&self, rhs: &Self) -> Fuel {
+        let linear_difference = if self > rhs {
+            self.0 - rhs.0
+        } else {
+            rhs.0 - self.0
+        };
+        Fuel(linear_difference * (linear_difference + 1) / 2)
+    }
+}
+
+#[derive(Default, Debug)]
+struct CrabSwarm {
+    crabs: Vec<CrabPosition>,
+}
+
+impl CrabSwarm {
+    fn new(mut crabs: Vec<CrabPosition>) -> CrabSwarm {
+        crabs.sort();
+        CrabSwarm { crabs }
+    }
+
+    fn linear_min_fuel_sum(&self) -> (CrabPosition, Fuel) {
+        (self.crabs[0].0..self.crabs[self.crabs.len() - 1].0)
+            .map(CrabPosition)
+            .map(|pos| {
+                (
+                    pos,
+                    self.crabs.iter().map(|crab| crab.linear_fuel(&pos)).sum(),
+                )
+            })
+            .min_by_key(|(_pos, fuel)| *fuel)
+            .expect("Expected at least one crab")
+    }
+
+    fn exponential_min_fuel_sum(&self) -> (CrabPosition, Fuel) {
+        (self.crabs[0].0..self.crabs[self.crabs.len() - 1].0)
+            .map(CrabPosition)
+            .map(|pos| {
+                (
+                    pos,
+                    self.crabs
+                        .iter()
+                        .map(|crab| crab.exponential_fuel(&pos))
+                        .sum(),
+                )
+            })
+            .min_by_key(|(_pos, fuel)| *fuel)
+            .expect("Expected at least one crab")
+    }
+}
+
+fn parse_swarm(input: &str) -> IResult<&str, CrabSwarm> {
+    map(
+        separated_list1(tag(","), map(nom_u64, CrabPosition)),
+        CrabSwarm::new,
+    )(input)
+}
-- 
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