2025 Day 3 (unclean version)

Author: hsaikia

src/bin/2025_03/main.rs

@@ -0,0 +1,93 @@
+use std::collections::HashMap;
+
+use aoc::common;
+
+fn find(bank: &[u64], i: usize, l: usize, mp: &mut HashMap<(usize, usize), u64>) -> Option<u64> {
+    if let Some(x) = mp.get(&(i, l)) {
+        return Some(*x);
+    }
+
+    if i >= bank.len() {
+        return None;
+    }
+
+    if l == 1 {
+        let mx = (i..bank.len()).map(|x| bank[x]).max().unwrap();
+        mp.insert((i, l), mx);
+        return Some(mx);
+    }
+
+    let x1 = if let Some(x) = find(bank, i + 1, l - 1, mp) {
+        Some(x + 10u64.pow(l as u32 - 1) * bank[i])
+    } else {
+        None
+    };
+
+    let x2 = if let Some(x) = find(bank, i + 1, l, mp) {
+        Some(x)
+    } else {
+        None
+    };
+    //dbg!(i, l, x1, x2);
+    if let Some(x) = x1 {
+        if let Some(y) = x2 {
+            mp.insert((i, l), x.max(y));
+            return Some(x.max(y));
+        } else {
+            mp.insert((i, l), x);
+            return Some(x);
+        }
+    } else {
+        if let Some(y) = x2 {
+            mp.insert((i, l), y);
+            return Some(y);
+        } else {
+            return None;
+        }
+    }
+}
+
+fn solve<const PART: usize>(input: &str) -> u64 {
+    let mut ans = 0;
+    for line in input.split("\n") {
+        if line.is_empty() {
+            continue;
+        }
+        let batteries = line
+            .trim()
+            .chars()
+            .map(|c| c.to_digit(10).unwrap_or(0) as u64)
+            .collect::<Vec<u64>>();
+        // let mut mx = 0;
+        // for (i, b1) in batteries.iter().enumerate() {
+        //     for b2 in batteries.iter().skip(i + 1) {
+        //         mx = mx.max(10 * b1 + b2);
+        //     }
+        // }
+        let mut mp: HashMap<(usize, usize), u64> = HashMap::new();
+        if let Some(mx) = find(&batteries, 0, if PART == 1 { 2 } else { 12 }, &mut mp) {
+            //dbg!(line, mx);
+            ans = ans + mx;
+        }
+    }
+    ans
+}
+
+fn main() {
+    if let Some(input) = common::get_input() {
+        common::timed(&input, solve::<1>, true);
+        common::timed(&input, solve::<2>, true);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_samples() {
+        let sample_input = "987654321111111\n811111111111119\n234234234234278\n818181911112111";
+        assert_eq!(solve::<1>(sample_input), 357);
+        assert_eq!(solve::<2>(sample_input), 3121910778619);
+    }
+}