2 files changed, 85 insertions, 0 deletions

diff --git a/2022/25/a.rs b/2022/25/a.rs
new file mode 100644
index 0000000..1d7e62b
--- /dev/null
+++ b/2022/25/a.rs
@@ -0,0 +1,13 @@
+mod common;
+use common::*;
+
+fn main() {
+    let mut line = String::new();
+    let mut sum = Snafu::zero();
+    while std::io::stdin().read_line(&mut line).unwrap() > 0 {
+        let s = Snafu::from_str(&line[..line.len()-1]);
+        sum += &s;
+        line.clear();
+    }
+    println!("{sum}");
+}
diff --git a/2022/25/common.rs b/2022/25/common.rs
new file mode 100644
index 0000000..de86470
--- /dev/null
+++ b/2022/25/common.rs
@@ -0,0 +1,72 @@
+use std::fmt;
+use std::ops;
+use std::cmp;
+
+pub struct Snafu {
+    d: Vec<i8>
+}
+
+impl Snafu {
+    const DIGITS: [char; 5] = ['=', '-', '0', '1', '2'];
+
+    fn digit_to_i8(c: char) -> i8 {
+        for i in 0..5 {
+            if c == Snafu::DIGITS[i] { return i as i8 - 2; }
+        }
+        panic!("Invalid Snafu digit '{}'", c);
+    }
+
+    fn i8_to_digit(i: i8) -> char {
+        if i < -2 || i > 2 {
+            panic!("Invalid Snafu digit value {}", i);
+        }
+        Snafu::DIGITS[(i + 2) as usize]
+    }
+
+    pub fn ndigits(&self) -> usize {
+        self.d.len()
+    }
+
+    pub fn zero() -> Snafu {
+        Snafu { d: vec![0] }
+    }
+
+    pub fn from_str(s: &str) -> Snafu {
+        let mut d = vec![];
+        for c in s.chars() { d.push(Self::digit_to_i8(c)); }
+        d.reverse();
+        Snafu { d }
+    }
+}
+
+impl fmt::Display for Snafu {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // Strip leading zeros
+        let mut n = self.ndigits()-1;
+        while self.d[n] == 0 { n -= 1; }
+
+        for i in (0..=n).rev() {
+            write!(f, "{}", Self::i8_to_digit(self.d[i]))?;
+        }
+        Ok(())
+    }
+}
+
+impl ops::AddAssign<&Snafu> for Snafu {
+    fn add_assign(&mut self, other: &Snafu) {
+        for i in 0..cmp::max(self.ndigits(), other.ndigits()) {
+            if i < other.ndigits() {
+                self.d[i] += other.d[i];
+            }
+
+            // Carry over, both ways
+            if i == self.ndigits()-1 { self.d.push(0); }
+            while self.d[i] > 2  { self.d[i+1] += 1; self.d[i] -= 5; }
+            while self.d[i] < -2 { self.d[i+1] -= 1; self.d[i] += 5; }
+        }
+
+        for i in 0..self.ndigits() {
+            if self.d[i] == 0 { self.d.pop(); } else { break; }
+        }
+    }
+}