Advent of code day 17, rough doing the decompilation

advent_of_code/2024/17/src/main.rs

@@ -0,0 +1,180 @@
+fn parse(input: &str) -> (u64, u64, u64, Vec<u64>) {
+    let lines: Vec<Vec<&str>> = input
+        .lines()
+        .map(|l| l.split_whitespace().collect())
+        .collect();
+
+    (
+        lines[0].last().unwrap().parse().unwrap(),
+        lines[1].last().unwrap().parse().unwrap(),
+        lines[2].last().unwrap().parse().unwrap(),
+        lines
+            .last()
+            .unwrap()
+            .last()
+            .unwrap()
+            .split(',')
+            .map(|i| i.parse().unwrap())
+            .collect(),
+    )
+}
+
+fn combo(a: u64, b: u64, c: u64, op: u64) -> u64 {
+    match op {
+        0 => 0,
+        1 => 1,
+        2 => 2,
+        3 => 3,
+        4 => a,
+        5 => b,
+        6 => c,
+        _ => unreachable!(),
+    }
+}
+
+fn solve_1(input: &str) -> String {
+    let (a, b, c, ops) = parse(input);
+
+    stringify(solve(a, b, c, ops))
+}
+
+fn solve(mut a: u64, mut b: u64, mut c: u64, ops: Vec<u64>) -> Vec<u64> {
+    let mut ip = 0;
+    let mut out: Vec<u64> = vec![];
+
+    while ip < ops.len() {
+        let ins = *ops.get(ip).unwrap();
+        let op = *ops.get(ip + 1).unwrap();
+        match ins {
+            0 => {
+                // adv
+                let result = a >> combo(a, b, c, op);
+                a = result;
+                ip += 2;
+            }
+            1 => {
+                // bxl
+                let result = b ^ op;
+                b = result;
+                ip += 2;
+            }
+            2 => {
+                // bst
+                let result = combo(a, b, c, op) % 8;
+                b = result;
+                ip += 2;
+            }
+            3 => {
+                // jnz
+                if a != 0 {
+                    ip = op as usize;
+                } else {
+                    ip += 2;
+                }
+            }
+            4 => {
+                // bxc
+                let result = b ^ c;
+                b = result;
+                ip += 2;
+            }
+            5 => {
+                // out
+                out.push(combo(a, b, c, op) % 8);
+                ip += 2;
+            }
+            6 => {
+                // bdv
+                let result = a >> combo(a, b, c, op);
+                b = result;
+                ip += 2;
+            }
+            7 => {
+                // cdv
+                let result = a >> combo(a, b, c, op);
+                c = result;
+                ip += 2;
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    out
+}
+
+fn stringify(ops: Vec<u64>) -> String {
+    let out = ops
+        .into_iter()
+        .fold("".to_string(), |result, n| result + "," + &n.to_string());
+
+    out.as_str()[1..].to_string()
+}
+
+// Decompilation of my program yields the following
+// 2,4,1,7,7,5,0,3,4,4,1,7,5,5,3,0
+//
+// while a:
+//     b = a % 8
+//     b = b ^ 7
+//     c = a >> b
+//     a = a >> 3
+//     b = b ^ c
+//     b = b ^ 7
+//     out(b % 8)
+
+fn solve_2(input: &str) -> u64 {
+    fn find(ops: &[u64], ans: u64) -> Option<u64> {
+        if ops.is_empty() {
+            return Some(ans);
+        }
+
+        for t in 0..8 {
+            let a = ans << 3 | t;
+
+            let mut b = a % 8;
+            b = b ^ 7;
+            let c = a >> b;
+            b = b ^ c;
+            b = b ^ 7;
+            let output = b % 8;
+
+            if output == *ops.last().unwrap() {
+                let sub = find(&ops[..ops.len() - 1], a);
+                if sub.is_some() {
+                    return sub;
+                }
+            }
+        }
+        return None;
+    }
+
+    let (_a, _b, _c, ops) = parse(input);
+
+    find(&ops[..], 0).unwrap()
+}
+
+fn main() {
+    println!("Hello, this is Patrick!");
+
+    let input = include_str!("../input.txt");
+
+    let result_1 = solve_1(input);
+    println!("The final output of the program is {}", result_1);
+
+    let result_2 = solve_2(input);
+    println!(
+        "The lowest positive initial value for register A to get a copy of the program is {}",
+        result_2
+    );
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1() {
+        let test_input = include_str!("../test.txt");
+        assert_eq!(solve_1(test_input), "4,6,3,5,6,3,5,2,1,0");
+    }
+}