From d8dab4ab95f68685c47f75e54323f425688c2568 Mon Sep 17 00:00:00 2001
From: LongHairedHacker <sebastian@sebastians-site.de>
Date: Tue, 15 Dec 2020 13:29:57 +0100
Subject: [PATCH] Added day 15

---
 inputs/day15.txt |  1 +
 inputs/test.txt  |  5 +----
 src/bin/day15.rs | 40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 4 deletions(-)
 create mode 100644 inputs/day15.txt
 create mode 100644 src/bin/day15.rs

diff --git a/inputs/day15.txt b/inputs/day15.txt
new file mode 100644
index 0000000..fe45c3e
--- /dev/null
+++ b/inputs/day15.txt
@@ -0,0 +1 @@
+5,1,9,18,13,8,0
diff --git a/inputs/test.txt b/inputs/test.txt
index 2e961e3..c84ffe7 100644
--- a/inputs/test.txt
+++ b/inputs/test.txt
@@ -1,4 +1 @@
-mask = 000000000000000000000000000000X1001X
-mem[42] = 100
-mask = 00000000000000000000000000000000X0XX
-mem[26] = 1
+0,3,6
diff --git a/src/bin/day15.rs b/src/bin/day15.rs
new file mode 100644
index 0000000..7630a99
--- /dev/null
+++ b/src/bin/day15.rs
@@ -0,0 +1,40 @@
+use itertools::Itertools;
+use std::collections::HashMap;
+use std::error::Error;
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::vec::Vec;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let file = File::open("inputs/day15.txt")?;
+    let mut lines = io::BufReader::new(file).lines();
+
+    let starting_numbers: Vec<u32> = lines
+        .nth(0)
+        .unwrap()
+        .unwrap()
+        .split(',')
+        .map(|n| n.parse().unwrap())
+        .collect();
+
+    let mut last_occurences: HashMap<u32, u32> = HashMap::new();
+
+    let mut last_number = *starting_numbers.first().unwrap();
+    for turn in 1..30000001 {
+        let spoken_number = if turn <= starting_numbers.len() {
+            starting_numbers[turn - 1]
+        } else if last_occurences.contains_key(&last_number) {
+            turn as u32 - last_occurences[&last_number]
+        } else {
+            0
+        };
+
+        last_occurences.insert(last_number, turn as u32);
+        //println!("Spoken number {} : {}", turn, spoken_number);
+        last_number = spoken_number;
+    }
+
+    println!("Last Number: {}", last_number);
+
+    Ok(())
+}