From ff8bc97329873ecdeb75c2acc4ed1ea7a21434f8 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Tue, 11 Dec 2018 10:31:23 +0100
Subject: [PATCH] Implement day 11 part 1.

---
 2018/inputs/11.txt |  1 +
 2018/src/day11.rs  | 61 +++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 2018/inputs/11.txt

diff --git a/2018/inputs/11.txt b/2018/inputs/11.txt
new file mode 100644
index 0000000..3cbd6fb
--- /dev/null
+++ b/2018/inputs/11.txt
@@ -0,0 +1 @@
+9435
diff --git a/2018/src/day11.rs b/2018/src/day11.rs
index bc80607..797af74 100644
--- a/2018/src/day11.rs
+++ b/2018/src/day11.rs
@@ -2,6 +2,15 @@ use std::io::Read;
 
 use common::Solution;
 
+fn power_at(serial: i32, (x, y): (i32, i32)) -> i32 {
+    let rack_id = x + 10;
+    let mut power_level = rack_id * y;
+    power_level += serial;
+    power_level *= rack_id;
+    power_level = (power_level % 1000) / 100;
+    power_level - 5
+}
+
 #[derive(Default)]
 pub struct Day11 {}
 
@@ -12,8 +21,37 @@ impl Day11 {
 }
 
 impl Solution for Day11 {
-    fn part1(&mut self, _input: &mut Read) -> String {
-        unimplemented!()
+    fn part1(&mut self, input: &mut Read) -> String {
+        let mut data = String::new();
+        input.read_to_string(&mut data).unwrap();
+        let serial = data.trim().parse().unwrap();
+
+        let mut best_coordinates: Option<(i32, i32)> = None;
+        let mut best_result = 0;
+
+        for y in 1..=298 {
+            let mut running_sum = 0;
+            let mut slide = [0i32;3];
+
+            for x in 1..298 {
+                let new_sum = (y..=(y+2)).map(|y| power_at(serial, (x, y))).sum();
+                running_sum += new_sum;
+
+                if x >= 3 {
+                    running_sum -= slide[(x as usize) % 3];
+                    if running_sum > best_result {
+                        best_result = running_sum;
+                        best_coordinates = Some((x - 2, y));
+                    }
+                }
+
+                slide[(x as usize) % 3] = new_sum;
+            }
+        }
+
+        let (x, y) = best_coordinates.unwrap();
+
+        format!("{},{}", x, y)
     }
 
     fn part2(&mut self, _input: &mut Read) -> String {
@@ -22,4 +60,21 @@ impl Solution for Day11 {
 }
 
 #[cfg(test)]
-mod tests {}
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_power_at() {
+        assert_eq!(4, power_at(8, (3, 5)));
+        assert_eq!(-5, power_at(57, (122, 79)));
+        assert_eq!(0, power_at(39, (217, 196)));
+        assert_eq!(4, power_at(71, (101, 153)));
+    }
+
+    #[test]
+    fn sample_part1() {
+        let mut instance = Day11::new();
+        assert_eq!("33,45", instance.part1(&mut b"18".as_ref()));
+        assert_eq!("21,61", instance.part1(&mut b"42".as_ref()));
+    }
+}