17th day

Author: majcn

data/examples/17.txt

@@ -0,0 +1,5 @@
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,3,5,5,3,0

src/bin/17.rs

@@ -0,0 +1,85 @@
+advent_of_code::solution!(17);
+
+use advent_of_code::maneatingape::parse::*;
+
+fn parse_data(input: &str) -> (u64, Vec<u8>) {
+    let (left, right) = input.split_once("\n\n").unwrap();
+
+    (left.unsigned(), right.iter_unsigned().collect())
+}
+
+fn run_program(a: u64) -> Vec<u8> {
+    let mut result = vec![];
+
+    let mut a = a;
+    while a > 0 {
+        let b = (a ^ 1) & 7;
+        result.push((((b ^ (a >> b)) ^ 4) & 7) as u8);
+
+        a >>= 3;
+    }
+
+    result
+}
+
+pub fn part_one(input: &str) -> Option<String> {
+    let (a, _) = parse_data(input);
+
+    let program_result = run_program(a);
+    let result_capacity = program_result.len() * 2;
+
+    let mut result = String::with_capacity(result_capacity);
+    for x in program_result {
+        result.push((b'0' + x) as char);
+        result.push(',');
+    }
+    result.pop();
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let (_, program) = parse_data(input);
+
+    let mut result = u64::MAX;
+
+    let mut queue = vec![];
+    queue.push((0, program.len() - 1));
+
+    while let Some((a, i)) = queue.pop() {
+        let p_i = program[i] as u64;
+
+        for part_a in 0..=7 {
+            let n_a = (a << 3) | (p_i ^ part_a ^ 5) << (part_a ^ 1) | part_a;
+
+            if i == 0 {
+                if run_program(n_a) == program {
+                    result = result.min(n_a);
+                }
+            } else {
+                if run_program(n_a) == program[i..] {
+                    queue.push((n_a, i - 1));
+                }
+            }
+        }
+    }
+
+    Some(result)
+}
+
+#[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(String::from("5,0,4,5")));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(188468));
+    }
+}