2 files changed, 110 insertions, 0 deletions
diff --git a/2020/rust/day02/Cargo.toml b/2020/rust/day02/Cargo.toml
new file mode 100644
index 0000000..56dd982
--- /dev/null
+++ b/2020/rust/day02/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day02"
+version = "0.1.0"
+authors = ["cos <cos>"]
+edition = "2018"
+
+[dependencies]
+aoc = { path = "../aoc" }
+anyhow = "1.0"
+itertools = "0.9"
diff --git a/2020/rust/day02/src/main.rs b/2020/rust/day02/src/main.rs
new file mode 100644
index 0000000..42e26e5
--- /dev/null
+++ b/2020/rust/day02/src/main.rs
@@ -0,0 +1,100 @@
+use anyhow::{Result, anyhow};
+use itertools::Itertools;
+use std::env::args;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::path::Path;
+use std::str::FromStr;
+
+#[derive(Debug)]
+struct PasswordPolicy {
+    character: char,
+    min: usize,
+    max: usize,
+}
+
+impl FromStr for PasswordPolicy {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut parts = s.split(' ');
+        let range = parts.next().ok_or_else(|| anyhow!("Could not find range: {}", s))?;
+        let character = parts.next().ok_or_else(|| anyhow!("Could not find char: {}", s))?
+            .chars().next().ok_or_else(|| anyhow!("Coult not parse char: {}", s))?;
+        let ( min, max ) = match range.split('-')
+            .map(|v| v.parse::<usize>()).collect::<Result<Vec<usize>, _>>()
+        {
+            Ok(vals) => {
+                vals.into_iter().collect_tuple().ok_or_else(|| anyhow!("Invalid range"))?
+            },
+            _ => return Err(anyhow!("Couldn't parse {}", s)),
+        };
+
+        Ok(PasswordPolicy { min, max, character })
+    }
+}
+
+impl From<&str> for PasswordPolicy {
+    fn from(s: &str) -> Self {
+        PasswordPolicy::from_str(s).expect(s)
+    }
+}
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<(PasswordPolicy, String)>> {
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+
+    reader.lines().map(|l| {
+        let line = l?;
+        let mut s = line.split(':');
+        let policy = From::from(s.next().ok_or_else(|| anyhow!("Could not parse policy"))?.trim());
+        let password = From::from(s.next()
+            .ok_or_else(|| anyhow!("Could not parse password"))?.trim());
+        Ok(( policy, password ))
+    }).collect()
+}
+
+fn part1(input: &[(PasswordPolicy, String)]) -> usize {
+    input.iter().filter(|row| {
+        let ( policy, password ) = row;
+        let occurances = password.chars().filter(|c| *c == policy.character).count();
+
+        occurances >= policy.min && occurances <= policy.max
+    }).count()
+}
+
+fn part2(input: &[(PasswordPolicy, String)]) -> usize {
+    input.iter().filter(|row| {
+        let ( policy, password ) = row;
+
+        let first = password.chars().nth(policy.min - 1);
+        let second = password.chars().nth(policy.max - 1);
+
+        first != second && (first == Some(policy.character) || second == Some(policy.character))
+    }).count()
+}
+
+fn main() {
+    let ( do_part_1, do_part_2 ) = aoc::do_parts();
+
+    let filename = match args().nth(1) {
+        Some(f) => f,
+        None => {
+            eprintln!("Missing input filename");
+            std::process::exit(1);
+        },
+    };
+    match read_input(filename) {
+        Ok(input) => {
+            if do_part_1 {
+                let solution = part1(&input);
+                println!("Part1, product found to be: {}", solution);
+            }
+            if do_part_2 {
+                let solution = part2(&input);
+                println!("Part2, product found to be: {}", solution);
+            }
+        },
+        Err(err) => eprintln!("Could not read input: {}", err),
+    }
+}