Implement 2022 day 25

2022/src/day25.rs

@@ -1,5 +1,71 @@
 use anyhow::Result;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+fn parse_num(num: &[u8]) -> Result<i64> {
+    let mut total = 0;
+    let mut factor = 1;
+
+    for &b in num.iter().rev() {
+        match b {
+            b'0' => (),
+            b'1' => total += factor,
+            b'2' => total += 2 * factor,
+            b'-' => total -= factor,
+            b'=' => total -= 2 * factor,
+            other => anyhow::bail!("Invalid digit {other}"),
+        }
+
+        factor *= 5;
+    }
+
+    Ok(total)
+}
+
+fn encode(mut num: i64) -> String {
+    let mut buffer = Vec::new();
+
+    while num > 0 {
+        match num % 5 {
+            0 => buffer.push(b'0'),
+            1 => buffer.push(b'1'),
+            2 => buffer.push(b'2'),
+            3 => {
+                buffer.push(b'=');
+                num += 2
+            }
+            4 => {
+                buffer.push(b'-');
+                num += 1;
+            }
+            _ => unreachable!("math"),
+        }
+
+        num /= 5;
+    }
+
+    // We've built the string right to left, to print we must reverse
+    buffer.reverse();
+
+    // Safe unwrap as we've only pushed valid ascii characters
+    String::from_utf8(buffer).unwrap()
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let total = input
+        .split(|&b| b == b'\n')
+        .map(parse_num)
+        .try_fold(0, |acc, val| val.map(|val| val + acc))?;
+
+    Ok(encode(total))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("./samples/25.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "2=-1=0");
+    }
 }

2022/src/samples/25.txt

@@ -0,0 +1,13 @@
+1=-0-2
+12111
+2=0=
+21
+2=01
+111
+20012
+112
+1=-1=
+1-12
+12
+1=
+122