From 59f78b90699386ba15a8a60821eba8b3b64e877f Mon Sep 17 00:00:00 2001
From: inga-lovinde <52715130+inga-lovinde@users.noreply.github.com>
Date: Sun, 20 Dec 2020 03:33:03 +0100
Subject: [PATCH] Solution for day 19

---
 day19/Cargo.toml  |  11 ++++
 day19/src/main.rs | 146 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 157 insertions(+)
 create mode 100644 day19/Cargo.toml
 create mode 100644 day19/src/main.rs

diff --git a/day19/Cargo.toml b/day19/Cargo.toml
new file mode 100644
index 0000000..4c7920a
--- /dev/null
+++ b/day19/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "day19"
+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]
+lazy_static = "1.4.0"
+regex = "1"
diff --git a/day19/src/main.rs b/day19/src/main.rs
new file mode 100644
index 0000000..7ed7d1a
--- /dev/null
+++ b/day19/src/main.rs
@@ -0,0 +1,146 @@
+use std::error::Error;
+use std::io::{self, BufRead};
+use std::str::FromStr;
+
+#[macro_use] extern crate lazy_static;
+use regex::Regex;
+
+enum Rule {
+    None,
+    Char(char),
+    Ref(usize),
+    Sequence(Vec<Rule>),
+    Choice(Vec<Rule>),
+}
+
+impl Default for Rule {
+    fn default() -> Self {
+        Rule::None
+    }
+}
+
+impl FromStr for Rule {
+    type Err = Box<dyn Error>;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        lazy_static! {
+            static ref CHAR_RE: Regex = Regex::new(r#"^"(\w)"$"#).unwrap();
+            static ref REF_RE: Regex = Regex::new(r"^(\d+)$").unwrap();
+            static ref CHOICE_SEPARATOR_RE: Regex = Regex::new(r"\s*\|\s*").unwrap();
+            static ref SEQ_SEPARATOR_RE: Regex = Regex::new(r"\s+").unwrap();
+        }
+
+        if let Some(char_captures) = CHAR_RE.captures(s) {
+            return Ok(Rule::Char(char_captures[1].chars().next().unwrap()));
+        }
+
+        if let Some(ref_captures) = REF_RE.captures(s) {
+            return Ok(Rule::Ref(ref_captures[1].parse()?));
+        }
+
+        if CHOICE_SEPARATOR_RE.is_match(s) {
+            return Ok(Rule::Choice(CHOICE_SEPARATOR_RE.split(s).map(|s| s.parse()).collect::<Result<_, _>>()?));
+        }
+
+        if SEQ_SEPARATOR_RE.is_match(s) {
+            return Ok(Rule::Sequence(SEQ_SEPARATOR_RE.split(s).map(|s| s.parse()).collect::<Result<_, _>>()?));
+        }
+
+        return Err(Box::from(format!("Failed to parse string '{}'", s)));
+    }
+}
+
+struct RuleWithIndex {
+    index: usize,
+    rule: Rule,
+}
+
+impl FromStr for RuleWithIndex {
+    type Err = Box<dyn Error>;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        lazy_static! {
+            static ref RULE_RE: Regex = Regex::new(r"^(\d+):\s*([\S].*)$").unwrap();
+        }
+
+        match RULE_RE.captures(s) {
+            Some(captures) => Ok(Self {
+                index: captures[1].parse()?,
+                rule: captures[2].parse()?,
+            }),
+            None => Err(Box::from(format!("Failed to parse string '{}'", s))),
+        }
+    }
+}
+
+fn get_match(rules: &[Rule], rule: &Rule, data: &[char], offset: usize) -> Vec<usize> {
+    match rule {
+        Rule::None => vec![],
+        Rule::Char(ch) => {
+            if offset < data.len() && data[offset] == *ch {
+                vec![offset + 1]
+            } else {
+                vec![]
+            }
+        },
+        Rule::Ref(rule_index) => get_match(&rules, &rules[*rule_index], &data, offset),
+        Rule::Sequence(rules_sequence) => {
+            let mut current_offsets = vec![offset];
+            for subrule in rules_sequence {
+                current_offsets = current_offsets.into_iter()
+                    .flat_map(|current_offset| get_match(&rules, subrule, &data, current_offset))
+                    .collect();
+            }
+
+            current_offsets
+        },
+        Rule::Choice(rules_choice) => rules_choice.iter()
+            .flat_map(|subrule| get_match(&rules, subrule, &data, offset))
+            .collect(),
+    }
+}
+
+fn is_match(rules: &[Rule], rule: &Rule, data: &[char]) -> bool {
+    get_match(&rules, &rule, &data, 0).contains(&data.len())
+}
+
+fn main() {
+    let stdin = io::stdin();
+    let mut lines = stdin.lock().lines().into_iter();
+    let mut rules_lines: Vec<RuleWithIndex> = Vec::new();
+    loop {
+        let line = lines.next().unwrap().unwrap();
+        if line == "" {
+            break;
+        }
+
+        rules_lines.push(line.parse().unwrap());
+    }
+
+    let mut rules: Vec<Rule> = Vec::new();
+    rules.resize_with(
+        rules_lines.iter().map(|rule_with_index| rule_with_index.index).max().unwrap() + 1,
+        Default::default
+    );
+    for rule_line in rules_lines {
+        rules[rule_line.index] = rule_line.rule;
+    }
+
+    let mut matches_count = 0;
+    loop {
+        match lines.next() {
+            Some(Ok(line)) => {
+                let result = is_match(&rules, &Rule::Ref(0), &line.chars().collect::<Vec<_>>());
+                println!("Match: {}", result);
+                if result {
+                    matches_count += 1;
+                }
+            }
+            _ => {
+                break;
+            }
+        }
+    }
+
+    println!("{}", matches_count);
+}