From 1a9abe8f952d8bd3168ca7241e2fb3e3436dad99 Mon Sep 17 00:00:00 2001
From: kageru <kageru@encode.moe>
Date: Wed, 9 Dec 2020 10:45:38 +0100
Subject: [PATCH] Add 2020/09

---
 2020/src/bin/day09.rs | 94 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 88 insertions(+), 6 deletions(-)

diff --git a/2020/src/bin/day09.rs b/2020/src/bin/day09.rs
index 5bf39f0..77ea1fc 100644
--- a/2020/src/bin/day09.rs
+++ b/2020/src/bin/day09.rs
@@ -2,18 +2,58 @@
 extern crate test;
 use std::env;
 
+use itertools::{Itertools, MinMaxResult};
+
 fn read_input() -> String {
-    std::fs::read_to_string(env::args().nth(1).filter(|n| n != "--bench").unwrap_or(String::from("inputs/day09"))).unwrap()
+    std::fs::read_to_string(
+        env::args()
+            .nth(1)
+            .filter(|n| n != "--bench")
+            .unwrap_or(String::from("inputs/day09")),
+    )
+    .unwrap()
 }
 
-fn parse_input(raw: &str) -> Vec<!> {
-    unimplemented!()
+fn parse_input(raw: &str) -> Vec<usize> {
+    raw.lines().map(|l| l.parse().unwrap()).collect()
+}
+
+fn part1(input: &[usize], window_size: usize) -> usize {
+    *input
+        .windows(window_size + 1)
+        .find_map(|xs| {
+            xs.last()
+                .filter(|last| !xs[..window_size].iter().tuple_combinations().any(|(a, b)| a + b == **last))
+        })
+        .unwrap()
+}
+
+fn part2(input: &[usize], bad_num: usize) -> usize {
+    (0..input.len()).find_map(|i| sum_up_to(&input[i..], bad_num)).unwrap()
+}
+
+fn sum_up_to(input: &[usize], n: usize) -> Option<usize> {
+    let mut acc = input[0];
+    for x in 1..input.len() {
+        acc += input[x];
+        if acc == n {
+            return match input[..x].iter().minmax() {
+                MinMaxResult::MinMax(min, max) => Some(min + max),
+                _ => unreachable!(),
+            };
+        }
+        if acc > n {
+            return None;
+        }
+    }
+    return None;
 }
 
 fn main() {
     let input = parse_input(&read_input());
-    println!("Part 1: {}", part1(&input));
-    println!("Part 2: {}", part2(&input));
+    let p1 = part1(&input, 25);
+    println!("Part 1: {}", p1);
+    println!("Part 2: {}", part2(&input, p1));
 }
 
 #[cfg(test)]
@@ -21,6 +61,48 @@ mod tests {
     use super::*;
     use test::black_box;
 
-    const TEST_INPUT: &str = "";
+    const TEST_INPUT: &str = "35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576";
 
+    #[test]
+    fn part1_test() {
+        let input = parse_input(TEST_INPUT);
+        assert_eq!(part1(&input, 5), 127);
+    }
+
+    #[test]
+    fn part2_test() {
+        let input = parse_input(TEST_INPUT);
+        assert_eq!(part2(&input, 127), 62);
+    }
+
+    #[bench]
+    fn bench_part1(b: &mut test::Bencher) {
+        let input = parse_input(&read_input());
+        b.iter(|| assert_eq!(part1(black_box(&input), 25), 393911906));
+    }
+
+    #[bench]
+    fn bench_part2(b: &mut test::Bencher) {
+        let input = parse_input(&read_input());
+        b.iter(|| assert_eq!(part2(black_box(&input), 393911906), 59341885));
+    }
 }