Day 2 part 1

src/bin/day2.rs

@@ -0,0 +1,108 @@
+use std::time::Instant;
+
+use aoc_2025::{load, print_res};
+use bstr::BString;
+use color_eyre::eyre::Context;
+
+type Parsed<'a> = Vec<(u64, u64)>;
+
+#[inline(never)]
+pub fn parsing(input: &BString) -> color_eyre::Result<Parsed<'_>> {
+    str::from_utf8(input)?
+        .trim()
+        .split(',')
+        .map(|r| {
+            let Some((left, right)) = r.split_once('-') else {
+                color_eyre::eyre::bail!("Invalid range: {r}");
+            };
+
+            Ok((
+                left.parse()
+                    .with_context(|| format!("While parsing left value `{left}`"))?,
+                right
+                    .parse()
+                    .with_context(|| format!("While parsing right value `{right}`"))?,
+            ))
+        })
+        .collect()
+}
+
+#[inline(never)]
+pub fn part1(input: Parsed) {
+    let mut invalid_id_sum = 0;
+
+    for (start, end) in input {
+        let mut s = start;
+        let mut e = end;
+        let mut mag_s = s.ilog10() + 1;
+        let mut mag_e = e.ilog10() + 1;
+
+        // All ranges are of an odd length
+        if mag_s % 2 == 1 && mag_s == mag_e {
+            continue;
+        }
+
+        // Reduce e such that it has an even number of digits
+        if mag_e % 2 == 1 {
+            mag_e -= 1;
+            e = 10u64.pow(mag_e) - 1;
+        }
+
+        if mag_s % 2 == 1 {
+            s = 10u64.pow(mag_s);
+            mag_s += 1;
+        }
+
+        // Right now we only handle ranges with the same span
+        if mag_s != mag_e {
+            panic!();
+        }
+
+        let half_mag = mag_s / 2;
+        let pow10 = 10u64.pow(half_mag);
+
+        let high_start = s / pow10;
+        let high_end = e / pow10;
+
+        for invalid_part in high_start..=high_end {
+            let invalid = invalid_part * pow10 + invalid_part;
+            if invalid < start {
+                continue
+            }
+
+            if invalid > end {
+                break
+            }
+
+            invalid_id_sum += invalid;
+        }
+    }
+
+    print_res!("Sum of invalid IDs: {invalid_id_sum}");
+}
+
+#[inline(never)]
+pub fn part2(input: Parsed) {
+    todo!("todo part2")
+}
+
+pub fn main() -> color_eyre::Result<()> {
+    let context = load()?;
+
+    let start = Instant::now();
+    let parsed = parsing(&context.input)?;
+    let elapsed = humantime::format_duration(start.elapsed());
+
+    let start = Instant::now();
+    if context.part == 1 {
+        part1(parsed);
+    } else {
+        part2(parsed);
+    }
+    let elapsed_part = humantime::format_duration(start.elapsed());
+
+    println!("  Parsing: {elapsed}");
+    println!("  Solving: {elapsed_part}");
+
+    Ok(())
+}