From 19dd107e45fcaa2b4c1cbeefb6bd79097f920724 Mon Sep 17 00:00:00 2001
From: Sebastian <sebastian@sebastians-site.de>
Date: Sun, 12 Dec 2021 15:25:19 +0100
Subject: [PATCH] Added day 12

---
 inputs/day12.txt  | 24 +++++++++++++
 inputs/sample.txt | 17 ++++-----
 src/bin/day12.rs  | 89 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 120 insertions(+), 10 deletions(-)
 create mode 100644 inputs/day12.txt
 create mode 100644 src/bin/day12.rs

diff --git a/inputs/day12.txt b/inputs/day12.txt
new file mode 100644
index 0000000..bc8429c
--- /dev/null
+++ b/inputs/day12.txt
@@ -0,0 +1,24 @@
+pg-CH
+pg-yd
+yd-start
+fe-hv
+bi-CH
+CH-yd
+end-bi
+fe-RY
+ng-CH
+fe-CH
+ng-pg
+hv-FL
+FL-fe
+hv-pg
+bi-hv
+CH-end
+hv-ng
+yd-ng
+pg-fe
+start-ng
+end-FL
+fe-bi
+FL-ks
+pg-start
diff --git a/inputs/sample.txt b/inputs/sample.txt
index 03743f6..6fd8c41 100644
--- a/inputs/sample.txt
+++ b/inputs/sample.txt
@@ -1,10 +1,7 @@
-5483143223
-2745854711
-5264556173
-6141336146
-6357385478
-4167524645
-2176841721
-6882881134
-4846848554
-5283751526
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end
diff --git a/src/bin/day12.rs b/src/bin/day12.rs
new file mode 100644
index 0000000..0eb36ea
--- /dev/null
+++ b/src/bin/day12.rs
@@ -0,0 +1,89 @@
+use std::collections::HashMap;
+use std::collections::HashSet;
+use std::error::Error;
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::vec::Vec;
+
+fn enumerate_ways(
+    start: &str,
+    end: &str,
+    vertices: &HashMap<String, HashSet<String>>,
+    mut path: Vec<String>,
+    mut allow_twice: bool,
+) -> u64 {
+    if start == end {
+        return 1;
+    }
+
+    if start.chars().all(|c| c.is_lowercase()) {
+        if path.iter().filter(|n| n == &&start).count() > 0 {
+            if !allow_twice {
+                return 0;
+            } else {
+                allow_twice = false;
+            }
+        }
+    }
+
+    path.push(start.to_string());
+
+    let mut ways = 0;
+
+    for neighbor in vertices[start].iter() {
+        if neighbor != "start" {
+            ways += enumerate_ways(neighbor, end, vertices, path.clone(), allow_twice);
+        }
+    }
+
+    ways
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let file = File::open("inputs/day12.txt")?;
+    let links: Vec<(String, String)> = io::BufReader::new(file)
+        .lines()
+        .map(|l| l.unwrap())
+        .map(|l| {
+            let mut ends = l.split('-');
+            (
+                ends.next().unwrap().to_string(),
+                ends.next().unwrap().to_string(),
+            )
+        })
+        .collect();
+
+    let mut vertices: HashMap<String, HashSet<String>> = HashMap::new();
+    for link in links.iter() {
+        if vertices.contains_key(&link.0) {
+            let mut set = vertices[&link.0].clone();
+            set.insert(link.1.clone());
+            vertices.insert(link.0.clone(), set);
+        } else {
+            let mut set: HashSet<String> = HashSet::new();
+            set.insert(link.1.clone());
+            vertices.insert(link.0.clone(), set);
+        }
+
+        if vertices.contains_key(&link.1) {
+            let mut set = vertices[&link.1].clone();
+            set.insert(link.0.clone());
+            vertices.insert(link.1.clone(), set);
+        } else {
+            let mut set: HashSet<String> = HashSet::new();
+            set.insert(link.0.clone());
+            vertices.insert(link.1.clone(), set);
+        }
+    }
+
+    let ways1 = enumerate_ways("start", "end", &vertices, Vec::new(), false);
+
+    println!("Answer1: {}", ways1);
+    println!("");
+
+    let ways2 = enumerate_ways("start", "end", &vertices, Vec::new(), true);
+
+    println!("Answer2: {}", ways2);
+
+    Ok(())
+}