Complete day 2

day-2/.gitignore

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+/target

day-2/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-2"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+]
+
+[[package]]
+name = "indoc"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47741a8bc60fb26eb8d6e0238bbb26d8575ff623fdc97b1a2c00c050b9684ed8"
+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce046d161f000fffde5f432a0d034d0341dc152643b2598ed5bfce44c4f3a8f0"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.53"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8833e20724c24de12bbaba5ad230ea61c3eafb05b881c7c9d3cfe8638b187e68"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
+name = "unindent"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f14ee04d9415b52b3aeab06258a3f07093182b88ba0f9b8d203f211a7a7d41c7"

day-2/Cargo.toml

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+[package]
+name = "day-2"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+[dependencies]
+indoc = "0.3"

day-2/src/main.rs

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+use std::fs;
+
+type PasswordPolicy = (usize, usize, char);
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("input")?;
+    println!("{}", count_valid_passwords(&input, &validate_password_new));
+    Ok(())
+}
+
+fn parse_password_line(line: &str) -> Result<(PasswordPolicy, &str), Box<dyn std::error::Error>> {
+    let mut sections = line.split(' ');
+    let range = sections
+        .next()
+        .ok_or("Password line too short")?
+        .split('-')
+        .map(|c| c.parse::<usize>())
+        .collect::<Result<Vec<usize>, _>>()?;
+
+    let character = sections
+        .next()
+        .ok_or("Password line too short")?
+        .chars()
+        .next()
+        .ok_or("Password line too short")?;
+    let password = sections.next().ok_or("Password line too short")?;
+
+    Ok(((range[0], range[1], character), password))
+}
+
+fn validate_password_old(policy: &PasswordPolicy, password: &str) -> bool {
+    let (start, end, character) = policy;
+
+    let occurrences = password.chars().filter(|c| c == character).count();
+    *start <= occurrences && occurrences <= *end
+}
+
+fn validate_password_new(policy: &PasswordPolicy, password: &str) -> bool {
+    let (position1, position2, character) = policy;
+    let position1_is_character = password
+        .chars()
+        .nth(position1 - 1)
+        .expect("Password too short")
+        == *character;
+    let position2_is_character = password
+        .chars()
+        .nth(position2 - 1)
+        .expect("Password too short")
+        == *character;
+
+    (position1_is_character || position2_is_character)
+        && (!position1_is_character || !position2_is_character)
+}
+
+fn count_valid_passwords(input: &str, validate: &dyn Fn(&PasswordPolicy, &str) -> bool) -> usize {
+    input
+        .lines()
+        .filter(|line| {
+            if let Ok((policy, password)) = parse_password_line(line) {
+                validate(&policy, password)
+            } else {
+                false
+            }
+        })
+        .count()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn test_simple() {
+        let example = indoc!(
+            "1-3 a: abcde
+             1-3 b: cdefg
+             2-9 c: ccccccccc"
+        );
+
+        assert_eq!(count_valid_passwords(&example, &validate_password_old), 2);
+    }
+
+    #[test]
+    fn test_simple2() {
+        let example = indoc!(
+            "1-3 a: abcde
+             1-3 b: cdefg
+             2-9 c: ccccccccc"
+        );
+
+        assert_eq!(count_valid_passwords(&example, &validate_password_new), 1);
+    }
+}