Solution for day 18

day18-hard/Cargo.toml

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+[package]
+name = "day18-hard"
+version = "0.1.0"
+authors = ["inga-lovinde <52715130+inga-lovinde@users.noreply.github.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "^4.2.3"
+nom-peg = "0.1.1"

day18-hard/src/main.rs

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+use std::io::{self, BufRead};
+
+#[macro_use]
+extern crate nom;
+extern crate nom_peg;
+use nom_peg::grammar;
+
+fn main() {
+    let arithmetic = grammar! {
+        parse: i64 = <expr> "="
+
+        expr: i64 = <l: sum> (" ")* "*" (" ")* <r: expr> => { l * r }
+                  | sum
+    
+        sum: i64 = <l: value> (" ")* "+" (" ")* <r: sum> => { l + r }
+                     | value
+    
+        value: i64 = ("0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9")+ => { result.join("").parse::<i64>().unwrap() }
+                   | "(" <expr> ")"
+    };
+
+    let mut result = 0;
+    let stdin = io::stdin();
+    for line in stdin.lock().lines() {
+        let value = arithmetic.parse(&(line.unwrap() + "=")).unwrap().1;
+        println!("{}", value);
+        result += value;
+    }
+
+    println!("{}", result)
+}

day18/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "day18"
+version = "0.1.0"
+authors = ["inga-lovinde <52715130+inga-lovinde@users.noreply.github.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "^4.2.3"
+nom-peg = "0.1.1"

day18/src/main.rs

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+use std::io::{self, BufRead};
+
+#[macro_use]
+extern crate nom;
+extern crate nom_peg;
+use nom_peg::grammar;
+
+fn main() {
+    let arithmetic = grammar! {
+        parse: i64 = <term> "="
+
+        term: i64 = <l: value> (" ")* "+" (" ")* <r: term> => { r + l }
+                  | <l: value> (" ")* "*" (" ")* <r: term> => { r * l }
+                  | value
+
+        value: i64 = ("0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9")+ => { result.join("").chars().rev().collect::<String>().parse::<i64>().unwrap() }
+            | ")" <term> "("
+    };
+
+    let mut result = 0;
+    let stdin = io::stdin();
+    for line in stdin.lock().lines() {
+        let value = arithmetic.parse(&(line.unwrap().chars().rev().collect::<String>() + "=")).unwrap().1;
+        println!("{}", value);
+        result += value;
+    }
+
+    println!("{}", result)
+}