From e05cb5c9f0d450f4d9cdae2d3f1582288deb750e Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Thu, 10 Dec 2020 09:15:32 +0100
Subject: [PATCH] Implementation day 10

---
 2020/inputs/10.txt    | 100 ++++++++++++++++++++++++++++++++++++++++++
 2020/samples/10.2.txt |  31 +++++++++++++
 2020/samples/10.txt   |  11 +++++
 2020/src/day10.rs     |  71 ++++++++++++++++++++++++++++++
 2020/src/lib.rs       |   2 +
 5 files changed, 215 insertions(+)
 create mode 100644 2020/inputs/10.txt
 create mode 100644 2020/samples/10.2.txt
 create mode 100644 2020/samples/10.txt
 create mode 100644 2020/src/day10.rs

diff --git a/2020/inputs/10.txt b/2020/inputs/10.txt
new file mode 100644
index 0000000..239293c
--- /dev/null
+++ b/2020/inputs/10.txt
@@ -0,0 +1,100 @@
+30
+73
+84
+136
+132
+117
+65
+161
+49
+68
+139
+46
+21
+127
+109
+153
+163
+160
+18
+22
+131
+146
+62
+113
+172
+150
+171
+98
+93
+130
+170
+59
+1
+110
+2
+55
+37
+44
+148
+102
+40
+28
+35
+43
+56
+169
+33
+5
+141
+83
+15
+105
+142
+36
+116
+11
+45
+82
+10
+17
+159
+140
+12
+108
+29
+72
+121
+52
+91
+166
+88
+97
+118
+99
+124
+149
+16
+9
+143
+104
+57
+79
+123
+58
+96
+24
+162
+23
+92
+69
+147
+156
+25
+133
+34
+8
+85
+76
+103
+122
diff --git a/2020/samples/10.2.txt b/2020/samples/10.2.txt
new file mode 100644
index 0000000..e6376dc
--- /dev/null
+++ b/2020/samples/10.2.txt
@@ -0,0 +1,31 @@
+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3
diff --git a/2020/samples/10.txt b/2020/samples/10.txt
new file mode 100644
index 0000000..ec4a03f
--- /dev/null
+++ b/2020/samples/10.txt
@@ -0,0 +1,11 @@
+16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4
diff --git a/2020/src/day10.rs b/2020/src/day10.rs
new file mode 100644
index 0000000..90015c4
--- /dev/null
+++ b/2020/src/day10.rs
@@ -0,0 +1,71 @@
+use std::io::Read;
+
+use crate::common::from_lines;
+use crate::Solution;
+
+#[derive(Default)]
+pub struct Day10;
+
+impl Solution for Day10 {
+    fn part1(&mut self, input: &mut dyn Read) -> String {
+        let mut adapters: Vec<u32> = from_lines(input);
+        // Outlet
+        adapters.push(0);
+        adapters.sort();
+        let device = *adapters.last().unwrap() + 3;
+        adapters.push(device);
+
+        let mut differences = [0u32; 4];
+
+        for window in adapters.windows(2) {
+            differences[(window[1] - window[0]) as usize] += 1;
+        }
+
+        (differences[1] * differences[3]).to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let mut adapters: Vec<u32> = from_lines(input);
+        adapters.push(0);
+        adapters.sort();
+
+        let mut methods = vec![0u64; adapters.len()];
+        methods[0] = 1;
+
+        for (i, a) in adapters.iter().copied().enumerate() {
+            let c = methods[i];
+
+            for (j, b) in adapters[i..].iter().enumerate().skip(1) {
+                if b - a <= 3 {
+                    methods[i + j] += c;
+                } else {
+                    break;
+                }
+            }
+        }
+
+        methods.last().unwrap().to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/10.txt");
+    const SAMPLE2: &[u8] = include_bytes!("../samples/10.2.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation!(Day10, 1, SAMPLE, 35);
+        test_implementation!(Day10, 1, SAMPLE2, 220);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation!(Day10, 2, SAMPLE, 8);
+        test_implementation!(Day10, 2, SAMPLE2, 19208);
+    }
+}
diff --git a/2020/src/lib.rs b/2020/src/lib.rs
index bc3265a..0ce4b52 100644
--- a/2020/src/lib.rs
+++ b/2020/src/lib.rs
@@ -10,6 +10,7 @@ mod day06;
 mod day07;
 mod day08;
 mod day09;
+mod day10;
 
 pub trait Solution {
     fn part1(&mut self, input: &mut dyn Read) -> String;
@@ -30,6 +31,7 @@ pub fn get_implementation(day: usize) -> Box<dyn Solution> {
         7 => Box::new(day07::Day07::default()),
         8 => Box::new(day08::Day08::default()),
         9 => Box::new(day09::Day09::default()),
+        10 => Box::new(day10::Day10::default()),
         _ => panic!("Unsupported day {}", day),
     }
 }