Day 7, part 1

5 files changed, 1229 insertions, 0 deletions

diff --git a/07/Cargo.toml b/07/Cargo.toml
new file mode 100644
index 0000000..8455c36
--- /dev/null
+++ b/07/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "day-07"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "part-1"
+path = "src/part-1.rs"
+
+#[[bin]]
+#name = "part-2"
+#path = "src/part-2.rs"
+
+[dependencies]
diff --git a/07/input.txt b/07/input.txt
new file mode 100644
index 0000000..10a5115
--- /dev/null
+++ b/07/input.txt
@@ -0,0 +1,1000 @@
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diff --git a/07/src/part-1.rs b/07/src/part-1.rs
new file mode 100644
index 0000000..920bae2
--- /dev/null
+++ b/07/src/part-1.rs
@@ -0,0 +1,33 @@
+mod stuff;
+
+use crate::stuff::{ascii_to_u64, read_helper, Card, Hand};
+
+
+fn main() {
+    let mut stdin = std::io::stdin().lock();
+
+    let mut buf: Vec<u8> = Vec::new();
+    let mut hands: Vec<(Hand, u64)> = Vec::new();
+
+    loop {
+        let num_bytes = read_helper(&mut stdin, &mut buf, b' ').expect("IO error");
+        if num_bytes == 0 { break; }
+        let cards: [Card; 5] = std::array::from_fn(|i| Card::try_from(buf[i]).expect("Malformed input"));
+        let hand = Hand::new(cards);
+
+        let num_bytes = read_helper(&mut stdin, &mut buf, b'\n').expect("IO error");
+        if num_bytes == 0 { panic!("Malformed input"); }
+        let bid: u64 = ascii_to_u64(& buf);
+
+        hands.push((hand, bid));
+    }
+
+    hands.sort_unstable_by(|(h1, _), (h2, _)| h1.cmp(h2));
+
+    let result: u64 = hands.into_iter()
+        .zip(1_u64..)
+        .map(|((_, bid), rank)| rank*bid)
+        .sum();
+
+    println!("{}", result);
+}
diff --git a/07/src/stuff.rs b/07/src/stuff.rs
new file mode 100644
index 0000000..25ee3ff
--- /dev/null
+++ b/07/src/stuff.rs
@@ -0,0 +1,177 @@
+use std::io::{BufRead};
+
+pub const NUM_CARDS: u8 = 13;
+
+pub fn ascii_to_u64(s: & [u8]) -> u64 {
+    #[cfg(debug_assertions)]
+    {
+        assert!(s.into_iter().all(|& c| c.is_ascii_digit()), "Not an ASCII base-10 number");
+    }
+
+    // SAFETY: AoC is ASCII-only.
+    unsafe { std::str::from_utf8_unchecked(s) }.parse().unwrap()
+}
+
+pub fn read_helper<'a, 'b, R: BufRead>(r: &'a mut R, buf: &'b mut Vec<u8>, token: u8) -> std::io::Result<usize> {
+    buf.clear();
+    let num_bytes = r.read_until(token, buf)?;
+    if buf.last() == Some(& token) { buf.pop(); }
+    Ok(num_bytes)
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Card {
+    A, K, Q, J, T,
+    Nine, Eight, Seven, Six, Five, Four, Three, Two
+}
+
+impl Card {
+    fn key(self: & Self) -> usize {
+        usize::from(self.value() - 2)
+    }
+    
+    pub fn value(self: & Self) -> u8 {
+        match self {
+            Self::Two => 2,
+            Self::Three => 3,
+            Self::Four => 4,
+            Self::Five => 5,
+            Self::Six => 6,
+            Self::Seven => 7,
+            Self::Eight => 8,
+            Self::Nine => 9,
+            Self::T => 10,
+            Self::J => 11,
+            Self::Q => 12,
+            Self::K => 13,
+            Self::A => 14
+        }
+    }
+}
+
+impl TryFrom<u8> for Card {
+    type Error = &'static str;
+
+    fn try_from(c: u8) -> Result<Self, Self::Error> {
+        match c {
+            b'A' => Ok(Self::A),
+            b'K' => Ok(Self::K),
+            b'Q' => Ok(Self::Q),
+            b'J' => Ok(Self::J),
+            b'T' => Ok(Self::T),
+            b'9' => Ok(Self::Nine),
+            b'8' => Ok(Self::Eight),
+            b'7' => Ok(Self::Seven),
+            b'6' => Ok(Self::Six),
+            b'5' => Ok(Self::Five),
+            b'4' => Ok(Self::Four),
+            b'3' => Ok(Self::Three),
+            b'2' => Ok(Self::Two),
+            _    => Err("ASCII character not a valid card")
+        }
+    }
+}
+
+impl PartialOrd for Card {
+    fn partial_cmp(self: & Self, other: & Self) -> Option<core::cmp::Ordering> {
+        self.value().partial_cmp(& other.value())
+    }
+}
+
+impl Ord for Card {
+    fn cmp(self: & Self, other: & Self) -> core::cmp::Ordering {
+        self.value().cmp(& other.value())
+    }
+}
+
+#[derive(Debug, Eq, PartialEq)]
+pub struct Hand {
+    cards: [Card; 5],
+    histogram: [u8; NUM_CARDS as usize]
+}
+
+impl Hand {
+    fn count(self: & Self, card: Card) -> u8 {
+        self.histogram[card.key()]
+    }
+    
+    pub fn new(cards: [Card; 5]) -> Self {
+        let mut histogram: [u8; NUM_CARDS as usize] = [0; NUM_CARDS as usize];
+        for card in cards.into_iter() {
+            histogram[card.key()] += 1;
+        }
+        Self { cards: cards, histogram: histogram }
+    }
+
+    pub fn is_n_of_a_kind(self: & Self, n: u8) -> bool {
+        self.histogram.into_iter().find(|& count| count == n).is_some()
+    }
+
+    pub fn is_full_house(self: & Self) -> bool {
+        self.is_n_of_a_kind(3) && self.is_n_of_a_kind(2)
+    }
+
+    pub fn is_two_pairs(self: & Self) -> bool {
+        self.histogram.into_iter()
+            .position(|count| count == 2)
+            .and_then(|i| (& self.histogram[i+1..]).into_iter()
+                      .position(|& count| count == 2))
+            .is_some()
+    }
+
+    pub fn strength(self: & Self) -> u8 {
+        if self.is_n_of_a_kind(5)      { 6 }
+        else if self.is_n_of_a_kind(4) { 5 }
+        else if self.is_full_house()   { 4 }
+        else if self.is_n_of_a_kind(3) { 3 }
+        else if self.is_two_pairs()    { 2 }
+        else if self.is_n_of_a_kind(2) { 1 }
+        else                           { 0 }
+    }
+}
+
+impl PartialOrd for Hand {
+    fn partial_cmp(self: & Self, other: & Self) -> Option<core::cmp::Ordering> {
+        let strength_ord = self.strength().cmp(& other.strength());
+        if strength_ord == core::cmp::Ordering::Equal {
+            Some(self.cards.cmp(& other.cards))
+        }
+        else {
+            Some(strength_ord)
+        }
+   }
+}
+
+impl Ord for Hand {
+    fn cmp(self: & Self, other: & Self) -> core::cmp::Ordering {
+        let strength_ord = self.strength().cmp(& other.strength());
+        if strength_ord == core::cmp::Ordering::Equal {
+            self.cards.cmp(& other.cards)
+        }
+        else {
+            strength_ord
+        }
+   }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1() {
+        let hand_1 = Hand::new([Card::Five, Card::Q, Card::Q, Card::Seven, Card::Five]);
+        let hand_2 = Hand::new([Card::Q, Card::Q, Card::T, Card::J, Card::Three]);
+        assert_eq!(hand_1.cmp(& hand_2), core::cmp::Ordering::Greater);
+    }
+
+    #[test]
+    fn two_pairs() {
+        assert!(Hand::new([Card::Five, Card::Q, Card::Q, Card::Seven, Card::Five]).is_two_pairs());
+    }
+
+    #[test]
+    fn two_pairs_2() {
+        assert!(Hand::new([Card::Three, Card::Three, Card::Four, Card::Four, Card::Seven]).is_two_pairs());
+    }
+}
diff --git a/07/test.txt b/07/test.txt
new file mode 100644
index 0000000..e3500c3
--- /dev/null
+++ b/07/test.txt
@@ -0,0 +1,5 @@
+32T3K 765
+T55J5 684
+KK677 28
+KTJJT 220
+QQQJA 483