Day 3

src/bin/day3.rs

@@ -0,0 +1,115 @@
+use std::time::Instant;
+
+use aoc_2025::{load, print_res};
+use bstr::{BStr, BString, ByteSlice};
+
+type Parsed<'a> = Vec<Bank<'a>>;
+
+const MAX_JOLT_LEN: usize = 12;
+
+pub struct Bank<'a> {
+    values: &'a BStr,
+    joltage_cache: [Vec<usize>; MAX_JOLT_LEN],
+}
+
+impl<'a> Bank<'a> {
+    fn max_joltage_from(&mut self, len: usize, from: usize) -> usize {
+        assert!(len <= MAX_JOLT_LEN);
+        assert!(len > 0);
+
+        if self.joltage_cache[len - 1][from] != 0 {
+            return self.joltage_cache[len - 1][from];
+        }
+
+        let &largest_hi = self
+            .values
+            .iter()
+            .take(self.values.len() - (len - 1))
+            .skip(from)
+            .max()
+            .unwrap();
+
+        if len == 1 {
+            let val = (largest_hi - b'0') as usize;
+            self.joltage_cache[len - 1][from] = val;
+            return val;
+        }
+
+        let mut max = 0;
+
+        for (i, _) in self
+            .values
+            .iter()
+            .enumerate()
+            .take(self.values.len() - (len - 1))
+            .skip(from)
+            .filter(|&(_, &v)| v == largest_hi)
+        {
+            let largest_low = self.max_joltage_from(len - 1, i + 1);
+
+            let joltage = (largest_hi - b'0') as usize * 10usize.pow(len as u32 - 1) + largest_low;
+            max = max.max(joltage);
+        }
+
+        self.joltage_cache[len - 1][from] = max;
+        max
+    }
+
+    pub fn max_joltage(&mut self, len: usize) -> usize {
+        self.max_joltage_from(len, 0)
+    }
+}
+
+#[inline(never)]
+pub fn parsing(input: &BString) -> color_eyre::Result<Parsed<'_>> {
+    Ok(input
+        .lines()
+        .map(|v| Bank {
+            values: v.as_bstr(),
+            joltage_cache: std::array::from_fn(|_| vec![0; v.len()]),
+        })
+        .collect())
+}
+
+#[inline(never)]
+pub fn part1(input: Parsed) {
+    let mut joltage_sum = 0;
+
+    for mut bank in input {
+        joltage_sum += bank.max_joltage(2);
+    }
+
+    print_res!("Maximum total joltage: {joltage_sum}");
+}
+
+#[inline(never)]
+pub fn part2(input: Parsed) {
+    let mut joltage_sum = 0;
+
+    for mut bank in input {
+        joltage_sum += bank.max_joltage(12);
+    }
+
+    print_res!("Maximum total joltage: {joltage_sum}");
+}
+
+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(())
+}