day-07 part-2

2024/day-06/input1.txt.2

@@ -1,10 +0,0 @@
-....#.....
-.........#
-..........
-..#.......
-.......#..
-..........
-.#..^.....
-........#.
-#.........
-......#...

2024/day-07/src/bin/part1.rs

@@ -7,6 +7,6 @@ fn main() -> Result<()> {
 
     let file = include_str!("../../input1.txt");
     let result = process(file).context("process part 1")?;
-    println!("{}", result);
+    println!("{result}");
     Ok(())
 }

2024/day-07/src/bin/part2.rs

@@ -7,6 +7,6 @@ fn main() -> Result<()> {
 
     let file = include_str!("../../input2.txt");
     let result = process(file).context("process part 2")?;
-    println!("{}", result);
+    println!("{result}");
     Ok(())
 }

2024/day-07/src/part1.rs

@@ -1,8 +1,6 @@
-use std::str::FromStr;
-
 use miette::{Diagnostic, Result};
+use std::str::FromStr;
 use thiserror::Error;
-use tracing::Instrument;
 
 #[derive(Debug, Clone, Copy)]
 enum Operator {
@@ -11,7 +9,7 @@ enum Operator {
 }
 
 impl Operator {
-    const fn apply(&self, a: usize, b: usize) -> usize {
+    const fn apply(self, a: usize, b: usize) -> usize {
         match self {
             Self::Add => a + b,
             Self::Multiply => a * b,

2024/day-07/src/part2.rs

@@ -1,9 +1,115 @@
-use miette::Result;
+use miette::{Diagnostic, Result};
+use std::str::FromStr;
+use thiserror::Error;
+
+#[derive(Debug, Clone, Copy)]
+enum Operator {
+    Add,
+    Multiply,
+    Concatenation,
+}
+
+impl Operator {
+    fn apply(self, a: usize, b: usize) -> usize {
+        match self {
+            Self::Add => a + b,
+            Self::Multiply => a * b,
+            Self::Concatenation => format!("{a}{b}").parse::<usize>().unwrap(),
+        }
+    }
+
+    const fn all_operators() -> [Self; 3] {
+        [Self::Add, Self::Multiply, Self::Concatenation]
+    }
+}
+
+#[derive(Debug, Error, Diagnostic)]
+enum EquationError {
+    #[error("Failed to parse equation")]
+    ParseError,
+    #[error("Missing value")]
+    MissingValue,
+}
+
+#[derive(Debug)]
+struct Equation {
+    result: usize,
+    numbers: Vec<usize>,
+}
+
+impl Equation {
+    fn find_result(&self) -> Option<usize> {
+        fn recursive_find(
+            numbers: &[usize],
+            target: usize,
+            current: usize,
+            index: usize,
+            is_first: bool,
+        ) -> Option<usize> {
+            if index == numbers.len() {
+                return if current == target {
+                    Some(current)
+                } else {
+                    None
+                };
+            }
+            let num = numbers[index];
+
+            for op in Operator::all_operators() {
+                if let Some(result) = recursive_find(
+                    numbers,
+                    target,
+                    if is_first {
+                        num
+                    } else {
+                        op.apply(current, num)
+                    },
+                    index + 1,
+                    false,
+                ) {
+                    return Some(result);
+                }
+            }
+
+            None
+        }
+        if self.numbers.is_empty() {
+            return None;
+        }
+        recursive_find(&self.numbers, self.result, 0, 0, true)
+    }
+}
+
+impl FromStr for Equation {
+    type Err = EquationError;
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        let line = s.trim().split(':').collect::<Vec<_>>();
+        let result = line
+            .first()
+            .ok_or(EquationError::MissingValue)?
+            .parse()
+            .map_err(|_| EquationError::ParseError)?;
+
+        let numbers = line
+            .last()
+            .ok_or(EquationError::MissingValue)?
+            .split_whitespace()
+            .map(str::parse)
+            .collect::<Result<Vec<usize>, _>>()
+            .map_err(|_| EquationError::ParseError)?;
+
+        Ok(Self { result, numbers })
+    }
+}
 
 #[tracing::instrument]
 pub fn process(input: &str) -> Result<usize> {
-    todo!("day xx - part 2");
-    Ok(0)
+    let result = input
+        .lines()
+        .map(Equation::from_str)
+        .filter_map(|eq| eq.ok()?.find_result())
+        .sum();
+    Ok(result)
 }
 
 #[cfg(test)]
@@ -12,9 +118,16 @@ mod tests {
 
     #[test]
     fn test_process() -> Result<()> {
-        let input = "";
-        todo!("haven't built test yet");
-        let result = 0;
+        let input = "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";
+        let result = 11387;
         assert_eq!(process(input)?, result);
         Ok(())
     }