2 files changed, 64 insertions, 1 deletions
diff --git a/2018/src/day7.rs b/2018/src/day7.rs
new file mode 100644
index 0000000..1924916
--- /dev/null
+++ b/2018/src/day7.rs
@@ -0,0 +1,61 @@
+use std::io;
+use std::io::BufRead;
+use std::cmp::Ordering;
+use std::collections::BinaryHeap;
+
+#[derive(PartialEq, Eq)]
+struct DecreasingU8(u8);
+
+impl PartialOrd for DecreasingU8 {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for DecreasingU8 {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.0.cmp(&self.0)
+    }
+}
+
+fn simulation(nexts: &[Vec<u8>], nelves: i32, basetime: i32, inctime: i32) -> (String, i32) {
+    let mut incoming = [0; 26];
+    for tos in nexts.iter() {
+        for &to in tos {
+            incoming[to as usize] += 1;
+        }
+    }
+
+    let mut sources = BinaryHeap::new();
+    for i in 0..26 {
+        if incoming[i as usize] == 0 {
+            sources.push(DecreasingU8(i));
+        }
+    }
+
+    let mut order = String::new();
+    while sources.len() > 0 {
+        let DecreasingU8(i) = sources.pop().unwrap();
+        order.push(char::from(i + 65));
+        for &to in &nexts[i as usize] {
+            incoming[to as usize] -= 1;
+            if incoming[to as usize] == 0 {
+                sources.push(DecreasingU8(to));
+            }
+        }
+    }
+
+    (order, 0)
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    let mut nexts: Vec<Vec<u8>> = vec![vec![]; 26];
+    for l in reader.lines().map(|l| l.unwrap()) {
+        let (from, to) = (l.as_bytes()[5] - 65, l.as_bytes()[36] - 65);
+        nexts[from as usize].push(to);
+    }
+
+    let (part1, _) = simulation(&nexts, 1, 1, 0);
+
+    Ok((part1, String::new()))
+}
diff --git a/2018/src/main.rs b/2018/src/main.rs
index c35e142..fccb319 100644
--- a/2018/src/main.rs
+++ b/2018/src/main.rs
@@ -15,8 +15,9 @@ mod day3;
 mod day4;
 mod day5;
 mod day6;
+mod day7;
 
-static NUM_DAYS: i32 = 6;
+static NUM_DAYS: i32 = 7;
 
 fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
     match day {
@@ -26,6 +27,7 @@ fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<(String, String)> {
         4 => day4::main(reader),
         5 => day5::main(reader),
         6 => day6::main(reader),
+        7 => day7::main(reader),
         _ => Err(Error::new(ErrorKind::Other, "Invalid day"))
     }
 }