Completed day 2

day2/src/main.rs

@@ -0,0 +1,112 @@
+use std::fs::File;
+use std::io::{self, prelude::*};
+
+const INPUT: &str = "input/input.txt";
+
+fn read_intcode(filename: &str) -> io::Result<Vec<i32>> {
+    let mut file = File::open(filename)?;
+    let mut intcode_string = String::new();
+    file.read_to_string(&mut intcode_string)?;
+    let intcode_string = intcode_string.trim().to_string();
+
+    Ok(intcode_string
+        .split(',')
+        .map(|code| code.parse().unwrap())
+        .collect())
+}
+
+fn run_intcode(intcode: &mut Vec<i32>) {
+    let mut pointer = 0;
+
+    loop {
+        match intcode[pointer] {
+            1 => {
+                let a = intcode[intcode[pointer + 1] as usize];
+                let b = intcode[intcode[pointer + 2] as usize];
+                let target = intcode[pointer + 3] as usize;
+                intcode[target] = a + b;
+            }
+            2 => {
+                let a = intcode[intcode[pointer + 1] as usize];
+                let b = intcode[intcode[pointer + 2] as usize];
+                let target = intcode[pointer + 3] as usize;
+                intcode[target] = a * b;
+            }
+            99 => {
+                break;
+            }
+            invalid => panic!("Invalid opcode: {}", invalid),
+        }
+
+        pointer += 4;
+    }
+}
+
+fn solve_part1() -> io::Result<i32> {
+    let mut intcode = read_intcode(INPUT)?;
+    intcode[1] = 12;
+    intcode[2] = 2;
+    run_intcode(&mut intcode);
+    Ok(intcode[0])
+}
+
+fn solve_part2() -> io::Result<i32> {
+    let original_intcode = read_intcode(INPUT)?;
+    for noun in 0..99 {
+        for verb in 0..99 {
+            let mut intcode = original_intcode.clone();
+            intcode[1] = noun;
+            intcode[2] = verb;
+            run_intcode(&mut intcode);
+            if intcode[0] == 19690720 {
+                return Ok(100 * noun + verb)
+            }
+        }
+    }
+    panic!("Could not find a noun and verb that produced the target value")
+}
+
+fn main() -> io::Result<()> {
+    println!("Part 1: {}", solve_part1()?);
+    println!("Part 2: {}", solve_part2()?);
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "input/test.txt";
+
+    #[test]
+    fn reads_intcode() {
+        assert_eq!(
+            read_intcode(TEST_INPUT).unwrap(),
+            vec![1, 9, 10, 3, 2, 3, 11, 0, 99, 30, 40, 50]
+        );
+    }
+
+    #[test]
+    fn runs_intcodes() {
+        let mut intcode = vec![1, 0, 0, 0, 99];
+        run_intcode(&mut intcode);
+        assert_eq!(intcode, vec![2, 0, 0, 0, 99]);
+
+        let mut intcode = vec![2, 3, 0, 3, 99];
+        run_intcode(&mut intcode);
+        assert_eq!(intcode, vec![2, 3, 0, 6, 99]);
+
+        let mut intcode = vec![2, 4, 4, 5, 99, 0];
+        run_intcode(&mut intcode);
+        assert_eq!(intcode, vec![2, 4, 4, 5, 99, 9801]);
+
+        let mut intcode = vec![1, 1, 1, 4, 99, 5, 6, 0, 99];
+        run_intcode(&mut intcode);
+        assert_eq!(intcode, vec![30, 1, 1, 4, 2, 5, 6, 0, 99]);
+
+        let mut intcode = vec![1, 9, 10, 3, 2, 3, 11, 0, 99, 30, 40, 50];
+        run_intcode(&mut intcode);
+        assert_eq!(intcode, vec![3500, 9, 10, 70, 2, 3, 11, 0, 99, 30, 40, 50]);
+    }
+}