From 1b2652a70d2e4a1bb6f50b69c2b6cf63827af823 Mon Sep 17 00:00:00 2001
From: kageru <kageru@encode.moe>
Date: Tue, 15 Dec 2020 10:21:03 +0100
Subject: [PATCH] Add 2020/15/1

---
 2020/inputs/day15     |  1 +
 2020/src/bin/day15.rs | 66 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 2020/inputs/day15
 create mode 100644 2020/src/bin/day15.rs

diff --git a/2020/inputs/day15 b/2020/inputs/day15
new file mode 100644
index 0000000..8285f9b
--- /dev/null
+++ b/2020/inputs/day15
@@ -0,0 +1 @@
+15,12,0,14,3,1
diff --git a/2020/src/bin/day15.rs b/2020/src/bin/day15.rs
new file mode 100644
index 0000000..9034bee
--- /dev/null
+++ b/2020/src/bin/day15.rs
@@ -0,0 +1,66 @@
+#![feature(test)]
+extern crate test;
+use std::collections::HashMap;
+
+type Parsed = Vec<usize>;
+
+fn read_input() -> String {
+    String::from("15,12,0,14,3,1")
+}
+
+fn parse_input(raw: &str) -> Parsed {
+    raw.split(',').filter_map(|x| x.parse().ok()).collect()
+}
+
+fn part1(parsed: &Parsed, limit: usize) -> usize {
+    let mut iter = parsed.iter();
+    let mut previous = HashMap::new();
+    let mut current = 0;
+    for i in 0..limit - 1 {
+        if let Some(&n) = iter.next() {
+            current = n;
+            previous.insert(current, i);
+            current = 0;
+            continue;
+        }
+        println!("Adding {} to {:?}", current, previous);
+        match previous.get(&current) {
+            Some(&position) => {
+                previous.insert(current, i);
+                current = i.saturating_sub(position);
+            }
+            None => {
+                previous.insert(current, i);
+                current = 0;
+            }
+        }
+    }
+    current
+}
+
+// only here so the test/bench macro works
+fn part2(parsed: &Parsed, limit: usize) -> usize {
+    part1(parsed, limit)
+}
+
+fn main() {
+    let input = parse_input(&read_input());
+    println!("Part 1: {}", part1(&input, 2020));
+    println!("Part 2: {}", part1(&input, 30000000));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use aoc2020::*;
+    use paste::paste;
+    use test::black_box;
+
+    const TEST_INPUT: &str = "0,3,6";
+
+    test!(part1(2020) == 436);
+    test!(part2(30000000) == 175594);
+    //bench!(part1() == 0);
+    //bench!(part2() == 0);
+    bench_input!(len == 6);
+}