From 59be8e9d7a4143d8ea789cf5deb11b1e17e269bb Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Tue, 11 Dec 2018 11:06:20 +0100
Subject: [PATCH] Implement day 11 part 2.

---
 2018/src/day11.rs | 61 ++++++++++++++++++++++++++++++++++-------------
 1 file changed, 44 insertions(+), 17 deletions(-)

diff --git a/2018/src/day11.rs b/2018/src/day11.rs
index 797af74..a69bb19 100644
--- a/2018/src/day11.rs
+++ b/2018/src/day11.rs
@@ -18,44 +18,64 @@ impl Day11 {
     pub fn new() -> Self {
         Default::default()
     }
-}
 
-impl Solution for Day11 {
-    fn part1(&mut self, input: &mut Read) -> String {
+    fn read_serial(&self, input: &mut Read) -> i32 {
         let mut data = String::new();
         input.read_to_string(&mut data).unwrap();
-        let serial = data.trim().parse().unwrap();
+        data.trim().parse().unwrap()
+    }
 
+    fn best(&self, serial: i32, size: i32) -> (i32, i32, i32) {
         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();
+        let mut slide = vec![0i32;size as usize];
+        let mut running_sum = 0;
+        for y in 1..=(301 - size) {
+            for x in 1..=300 {
+                let new_sum = (y..(y+size)).map(|y| power_at(serial, (x, y))).sum();
+                running_sum -= slide[(x % size) as usize];
                 running_sum += new_sum;
+                slide[(x % size) as usize] = new_sum;
 
-                if x >= 3 {
-                    running_sum -= slide[(x as usize) % 3];
+                if x >= size {
                     if running_sum > best_result {
                         best_result = running_sum;
-                        best_coordinates = Some((x - 2, y));
+                        best_coordinates = Some((x + 1 - size, y));
                     }
                 }
-
-                slide[(x as usize) % 3] = new_sum;
             }
         }
 
         let (x, y) = best_coordinates.unwrap();
 
+        (x, y, best_result)
+    }
+}
+
+impl Solution for Day11 {
+    fn part1(&mut self, input: &mut Read) -> String {
+        let serial = self.read_serial(input);
+        let (x, y, _) = self.best(serial, 3);
+
         format!("{},{}", x, y)
     }
 
-    fn part2(&mut self, _input: &mut Read) -> String {
-        unimplemented!()
+    fn part2(&mut self, input: &mut Read) -> String {
+        let serial = self.read_serial(input);
+        let mut best_result = 0;
+        let mut best_option = None;
+        for size in 1..=300 {
+            let (x, y, result) = self.best(serial, size);
+            if result > best_result {
+                best_result = result;
+                best_option = Some((x, y, size));
+            } else if result < best_result {
+                break;
+            }
+        }
+        let (x, y, size) = best_option.unwrap();
+        format!("{},{},{}", x, y, size)
     }
 }
 
@@ -77,4 +97,11 @@ mod tests {
         assert_eq!("33,45", instance.part1(&mut b"18".as_ref()));
         assert_eq!("21,61", instance.part1(&mut b"42".as_ref()));
     }
+
+    #[test]
+    fn sample_part2() {
+        let mut instance = Day11::new();
+        assert_eq!("90,269,16", instance.part2(&mut b"18".as_ref()));
+        assert_eq!("232,251,12", instance.part2(&mut b"42".as_ref()));
+    }
 }