From fe66170e3edd28c0c2a58ce38ef17bd243e2b498 Mon Sep 17 00:00:00 2001
From: "max.nuding" <max.nuding@uni-konstanz.de>
Date: Fri, 9 Dec 2022 08:46:16 +0100
Subject: [PATCH] Simulate chains simultaneously

---
 src/day09/mod.rs | 84 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 56 insertions(+), 28 deletions(-)

diff --git a/src/day09/mod.rs b/src/day09/mod.rs
index 8a2c6fe..34bc8e3 100644
--- a/src/day09/mod.rs
+++ b/src/day09/mod.rs
@@ -1,5 +1,6 @@
 use crate::read;
 use std::collections::HashSet;
+use itertools::Itertools;
 
 #[derive(Debug, PartialEq, Eq, Default, Clone, Hash)]
 struct Position {
@@ -59,43 +60,70 @@ impl Position {
     }
 }
 
+struct Chain {
+    pub knots: Vec<Position>,
+    visited: HashSet<Position>
+}
+
+impl Chain {
+    pub fn new(num_knots: usize) -> Self {
+        Self {
+            knots: vec![Position::default(); num_knots],
+            visited: HashSet::with_capacity(10000)
+        }
+    }
+    pub fn num_visited(&self) -> usize {
+        self.visited.len()
+    }
+
+    pub fn move_knots(&mut self, direction: &str, count: usize) {
+        let move_head_func = match direction {
+            "R" => Position::move_right,
+            "U" => Position::move_up,
+            "L" => Position::move_left,
+            "D" => Position::move_down,
+            _ => unreachable!(),
+        };
+        for _c in 0..count {
+            self.knots[0] = move_head_func(&mut self.knots[0]);
+            for i in 1..self.knots.len() {
+                self.knots[i] = self.knots[i].follow_head(&self.knots[i - 1]);
+            }
+
+            self.visited.insert(self.knots.last().unwrap().clone());
+        }
+    }
+}
+
 pub fn run() {
+    let res = simulate(vec![2, 10]);
     #[cfg(feature = "part1")]
     {
-        println!("Day 9, Part 01: {}", simulate(2));
+        println!("Day 9, Part 01: {}", res[0]);
     }
 
     #[cfg(feature = "part2")]
     {
-        println!("Day 9, Part 02: {}", simulate(10));
+        println!("Day 9, Part 02: {}", res[1]);
     }
 }
-pub fn simulate(num_knots: usize) -> usize {
-    let mut visited: HashSet<Position> = HashSet::new();
-    let mut knots = vec![Position::default(); num_knots];
 
-    let input = read("09");
-    let lines = input.lines();
-    for line in lines {
-        if line.is_empty() {
-            continue;
-        }
-        let (dir, count) = line.split_once(' ').unwrap();
-        let count = count.parse().unwrap();
-        for _c in 0..count {
-            knots[0] = match dir {
-                "R" => knots[0].move_right(),
-                "U" => knots[0].move_up(),
-                "L" => knots[0].move_left(),
-                "D" => knots[0].move_down(),
-                _ => unreachable!(),
-            };
-            for i in 1..knots.len() {
-                knots[i] = knots[i].follow_head(&knots[i - 1]);
-            }
+fn simulate(chain_sizes: Vec<usize>) -> Vec<usize> {
+    let chains = read("09")
+        .lines()
+        .filter(|l|!l.is_empty())
+        .map(|l|l.split_once(' ').unwrap())
+        .map(|(dir, count)|(dir, count.parse::<usize>().unwrap()))
+        .fold(chain_sizes
+                  .iter()
+                  .map(|c|Chain::new(*c))
+                  .collect_vec(),
+              |mut chains, (dir, count)| {
 
-            visited.insert(knots.last().unwrap().clone());
-        }
-    }
-    visited.len()
+            chains
+                .iter_mut()
+                .for_each(|chain|chain.move_knots(dir, count));
+            chains
+        });
+    chains.iter().map(|c|c.num_visited()).collect()
 }