From c7f40fe8a3083555d85afe6715e783ab23e48c4a Mon Sep 17 00:00:00 2001
From: Greg Burri <greg.burri@gmail.com>
Date: Sun, 5 Dec 2021 23:55:27 +0100
Subject: [PATCH] Day 3 part 1

---
 Cargo.toml   |  2 +-
 src/day02.rs |  2 +-
 src/day03.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |  8 ++++++++
 4 files changed, 64 insertions(+), 2 deletions(-)
 create mode 100644 src/day03.rs

diff --git a/Cargo.toml b/Cargo.toml
index 5e26f12..81eeff7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "advent_of_code_2021"
 version = "0.1.0"
 authors = ["Greg Burri <greg.burri@gmail.com>"]
-edition = "2018"
+edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
diff --git a/src/day02.rs b/src/day02.rs
index 732d179..cef65c3 100644
--- a/src/day02.rs
+++ b/src/day02.rs
@@ -22,7 +22,7 @@ pub fn parse_movements(movements: &str) -> Vec<Movement> {
                 "forward" => Movement::Forward(distance),
                 "down" => Movement::Down(distance),
                 "up" => Movement::Up(distance),
-                _ => Movement::Forward(0)
+                unknown_command => panic!("Unknown command: {}", unknown_command),
             }
         })
         .collect()
diff --git a/src/day03.rs b/src/day03.rs
new file mode 100644
index 0000000..fff84d8
--- /dev/null
+++ b/src/day03.rs
@@ -0,0 +1,54 @@
+use std::iter::Iterator;
+
+type Diagnostic = Vec<Vec<char>>;
+
+pub fn parse(diagnostic: &str) -> Diagnostic {
+    diagnostic
+        .split('\n')
+        .map(|line| { line.trim().chars().collect() })
+        .collect()
+}
+
+pub fn gamma_and_epsilon_rates(diagnostic: &Diagnostic) -> (u16, u16) {
+    let l = diagnostic[0].len();
+    dbg!(l);
+    let mut gamma = 0u16;
+    for i in 0..l {
+        if diagnostic.iter().fold(0, |n, current| { n + if current[i] == '1' { 1 } else { 0 } }) > diagnostic.len() / 2 {
+            gamma |= 1;
+        }
+
+        if i < l - 1 {
+            gamma <<= 1;
+        }
+    }
+
+    (gamma, !gamma & 0xFFFFu16 >> (16 - l))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1() {
+        let diagnostic =
+            parse(
+                "00100
+                11110
+                10110
+                10111
+                10101
+                01111
+                00111
+                11100
+                10000
+                11001
+                00010
+                01010"
+            );
+        let (gamma, epsilon) = gamma_and_epsilon_rates(&diagnostic);
+        assert_eq!(gamma, 22);
+        assert_eq!(epsilon, 9);
+    }
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index e3a099a..27fb5db 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -5,6 +5,7 @@ use std::time::Instant;
 mod common;
 mod day01;
 mod day02;
+mod day03;
 
 fn day01() -> String {
     let report = common::read_list_of_numbers("data/day01.input", "\n");
@@ -17,6 +18,12 @@ fn day02() -> String {
     format!("part1: {}, part2: {}", final_position.horizontal * final_position.aim, final_position.horizontal * final_position.depth)
 }
 
+fn day03() -> String {
+    let diagnostic = day03::parse(&fs::read_to_string("data/day03.input").unwrap());
+    let (gamma, epsilon) = day03::gamma_and_epsilon_rates(&diagnostic);
+    format!("part1: {}, part2: {}", gamma as u32 * epsilon as u32, "")
+}
+
 fn format_micros(t: u128) -> String {
     if t < 10_000 {
         format!("{} μs", t)
@@ -38,6 +45,7 @@ fn main() {
     let days: Vec<fn() -> String> = vec!(
         day01,
         day02,
+        day03,
     );
 
     let args: Vec<String> = env::args().skip(1).collect();
-- 
2.45.2