1 files changed, 73 insertions, 0 deletions
diff --git a/2018/src/day10.rs b/2018/src/day10.rs
new file mode 100644
index 0000000..28da8de
--- /dev/null
+++ b/2018/src/day10.rs
@@ -0,0 +1,73 @@
+use std::io;
+use std::io::BufRead;
+use std::collections::HashSet;
+
+fn parse_pt(l: &str) -> ((i32, i32), (i32, i32)) {
+    let i1 = l.find('<').unwrap();
+    let i2 = l[i1..].find(',').unwrap() + i1;
+    let i3 = l[i2..].find('>').unwrap() + i2;
+    let i4 = l[i3..].find('<').unwrap() + i3;
+    let i5 = l[i4..].find(',').unwrap() + i4;
+    let i6 = l[i5..].find('>').unwrap() + i5;
+
+    let s1 = &l[i1+1..i2];
+    let s2 = &l[i2+1..i3];
+    let s3 = &l[i4+1..i5];
+    let s4 = &l[i5+1..i6];
+
+    ((s1.trim().parse().unwrap(), s2.trim().parse().unwrap()),
+        (s3.trim().parse().unwrap(), s4.trim().parse().unwrap()))
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<(String, String)> {
+    let dots: Vec<((i32, i32), (i32, i32))> =
+        reader.lines().map(|l| l.unwrap())
+            .map(|l| parse_pt(&l))
+            .collect();
+
+    let mut pts: Vec<_> = dots.iter().map(|&(xy, _)| xy).collect();
+    let vels: Vec<_> = dots.iter().map(|&(_, v)| v).collect();
+
+    let mut maxscore = -1;
+    let mut maxat = (-1, vec![], HashSet::new());
+    for iter in 0..20000 {
+        let mut has_dot: HashSet<(i32, i32)> = HashSet::new();
+        let mut score = 0;
+        for &xy in &pts {
+            if has_dot.contains(&xy) { score += 1; }
+            has_dot.insert(xy);
+        }
+
+        if score > maxscore {
+            maxscore = score;
+            maxat = (iter, pts.clone(), has_dot.clone());
+            if maxscore > dots.len() as i32 / 2 {
+                break;
+            }
+        }
+
+        for i in 0..dots.len() {
+            pts[i].0 += vels[i].0;
+            pts[i].1 += vels[i].1;
+        }
+    }
+
+    let mut part1 = String::new();
+
+    let part2 = maxat.0.to_string();
+    let pts = maxat.1;
+    let has_dot = maxat.2;
+    let minx = pts.iter().map(|&(x, _)| x).min().unwrap();
+    let miny = pts.iter().map(|&(_, y)| y).min().unwrap();
+    let maxx = pts.iter().map(|&(x, _)| x).max().unwrap();
+    let maxy = pts.iter().map(|&(_, y)| y).max().unwrap();
+    for y in miny..maxy+1 {
+        if y != miny { part1 += "\n"; }
+        for x in minx..maxx + 1 {
+            if has_dot.contains(&(x, y)) { part1 += "#"; }
+            else { part1 += "."; }
+        }
+    }
+
+    Ok((part1, part2))
+}