Added day 15

inputs/day15.txt

@@ -0,0 +1 @@
+5,1,9,18,13,8,0

inputs/test.txt

@@ -1,4 +1 @@
-mask = 000000000000000000000000000000X1001X
-mem[42] = 100
-mask = 00000000000000000000000000000000X0XX
-mem[26] = 1
+0,3,6

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(())
+}