day 18 solutions

Signed-off-by: Stephen Waits <swaits@amazon.com>

src/day18.rs

@@ -0,0 +1,47 @@
+// ==== day 18
+
+use crate::utils;
+use anyhow::{anyhow, Result};
+
+peg::parser! {
+    grammar arithmetic_parser() for str {
+        rule ws() = quiet!{[' ' | '\n' | '\t']+}
+
+        rule number() -> i64
+            = n:$(['0'..='9']+) { n.parse().unwrap() }
+
+        pub rule arith_equal_precedence() -> i64 = precedence!{
+            x:(@) "+" y:@ { x + y }
+            x:(@) "*" y:@ { x * y }
+            --
+            ws()* n:number() ws()* { n }
+            ws()* "(" ws()* e:arith_equal_precedence() ws()* ")" ws()* { e }
+        }
+
+        pub rule arith_addition_precedence() -> i64 = precedence!{
+            x:(@) "*" y:@ { x * y }
+            --
+            x:(@) "+" y:@ { x + y }
+            --
+            ws()* n:number() ws()* { n }
+            ws()* "(" ws()* e:arith_addition_precedence() ws()* ")" ws()* { e }
+        }
+    }
+}
+
+// main
+pub fn run() -> Result<(i64, i64)> {
+    let data = utils::read_file("data/input-18.txt")?;
+    let answers = utils::read_i64s("data/output-18.txt")?;
+
+    let p1 = data.lines().fold(0, |sum, line| {
+        sum + arithmetic_parser::arith_equal_precedence(line).unwrap()
+    });
+    let p2 = data.lines().fold(0, |sum, line| {
+        sum + arithmetic_parser::arith_addition_precedence(line).unwrap()
+    });
+
+    assert_eq!(p1, answers[0]);
+    assert_eq!(p2, answers[1]);
+    Ok((p1, p2))
+}

src/main.rs

@@ -16,16 +16,9 @@ mod day13;
 mod day14;
 mod day15;
 mod day16;
+mod day18;
 mod utils;
 
-// TODO
-// ====
-// * clean up error handling (move to `?` inside closures)
-// * templatize read_i64s()
-// * build out a bit of a harness for the runner
-// * add criterion benchmarking
-// * figure out nicer way to organize into modules
-
 // ==== main()
 
 fn main() -> Result<()> {