Day 7

Author: jacob-greenfield

data/examples/07.txt

@@ -0,0 +1,9 @@
+190: 10 19
+3267: 81 40 27
+83: 17 5
+156: 15 6
+7290: 6 8 6 15
+161011: 16 10 13
+192: 17 8 14
+21037: 9 7 18 13
+292: 11 6 16 20

src/bin/07.rs

@@ -0,0 +1,102 @@
+use advent_of_code::template::parse::lines;
+
+advent_of_code::solution!(7);
+
+fn dfs1(target: u64, prior: u64, eqn: &[u64]) -> bool {
+    match eqn.split_first() {
+        None => prior == target,
+        Some((x, tail)) => dfs1(target, prior + x, tail) || dfs1(target, prior * x, tail),
+    }
+}
+
+const POW10: &[u64] = &[
+    1,
+    10,
+    100,
+    1_000,
+    10_000,
+    100_000,
+    1_000_000,
+    10_000_000,
+    100_000_000,
+    1_000_000_000,
+    10_000_000_000,
+    100_000_000_000,
+    1_000_000_000_000,
+    10_000_000_000_000,
+    100_000_000_000_000,
+    1_000_000_000_000_000,
+    10_000_000_000_000_000,
+    100_000_000_000_000_000,
+    1_000_000_000_000_000_000,
+    10_000_000_000_000_000_000,
+];
+
+fn dfs2(target: u64, prior: u64, eqn: &[(u64, usize)]) -> bool {
+    prior <= target
+        && match eqn.split_first() {
+            None => prior == target,
+            Some((&(x, len), tail)) => {
+                dfs2(target, prior + x, tail)
+                    || dfs2(target, prior * x, tail)
+                    || dfs2(target, (prior * POW10[len]) + x, tail)
+            }
+        }
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let mut res = 0;
+    for line in lines(input) {
+        let mut splita = line.split(':');
+        let target = splita.next().unwrap().parse::<u64>().unwrap();
+        let rest = splita.next().unwrap();
+        let eqn = rest
+            .split(' ')
+            .filter(|s| !s.is_empty())
+            .map(|s| s.parse::<u64>().unwrap())
+            .collect::<Vec<u64>>();
+        let (&init, tail) = eqn.split_first().unwrap();
+        if dfs1(target, init, tail) {
+            res += target;
+        }
+    }
+
+    Some(res)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut res = 0;
+    for line in lines(input) {
+        let mut splita = line.split(':');
+        let target = splita.next().unwrap().parse::<u64>().unwrap();
+        let rest = splita.next().unwrap();
+        let eqn = rest
+            .split(' ')
+            .filter(|s| !s.is_empty())
+            .map(|s| (s.parse::<u64>().unwrap(), s.len()))
+            .collect::<Vec<(u64, usize)>>();
+        let (&(init, _), tail) = eqn.split_first().unwrap();
+        if dfs2(target, init, tail) {
+            res += target;
+        }
+    }
+
+    Some(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3749));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(11387));
+    }
+}