1 files changed, 185 insertions, 0 deletions
diff --git a/16/src/main.rs b/16/src/main.rs
new file mode 100644
index 0000000..10c5877
--- /dev/null
+++ b/16/src/main.rs
@@ -0,0 +1,185 @@
+use advent_lib::prelude::*;
+
+use std::collections::BTreeMap;
+use std::collections::BTreeSet;
+
+#[derive(Clone,Debug)]
+struct Range {
+  min: i64,
+  max: i64,
+}
+
+
+fn main() -> Result<()> {
+  let mut args = std::env::args();
+  if args.len() != 2 {
+    eprintln!("Usage: advent input");
+  }
+  let _ = args.next();
+  let filename = args.next().unwrap();
+
+  let input = advent_lib::read_lines_file(&filename)?;
+  let input = advent_lib::group_lines_by_blanks(input);
+
+  let mut rules: BTreeMap<String,Vec<Range>> = BTreeMap::new();
+
+  for line in &input[0] {
+    let colon_point = line.find(':').unwrap();
+    let (field_name, rest) = line.split_at(colon_point);
+    let (_, rest) = rest.split_at(2);
+
+    let mut ranges: Vec<Range> = Vec::new();
+    for word in rest.split(' ') {
+      if word == "or" {
+        continue;
+      }
+
+      let parts: Vec<&str> = word.split('-').collect();
+      ranges.push(Range {
+        min: parts[0].parse::<i64>().unwrap(),
+        max: parts[1].parse::<i64>().unwrap(),
+      });
+
+    }
+    rules.insert(field_name.to_string(), ranges);
+  }
+
+  let player_ticket = parse_comma_separated_ints(&input[1][1]);
+
+  let mut nearby_tickets = Vec::new();
+  for line in input[2].iter().skip(1) {
+    nearby_tickets.push(parse_comma_separated_ints(&line));
+  }
+
+  let mut valid_tickets = Vec::new();
+  valid_tickets.push(player_ticket.clone());
+
+  let mut error_sum = 0;
+  for ticket in &nearby_tickets {
+    let mut is_valid = true;
+    for value in ticket {
+      let mut found_match = false;
+      for rule in rules.values() {
+        if value_obeys_rule(*value, rule) {
+          found_match = true;
+          break;
+        }
+      }
+
+      if !found_match {
+        error_sum += value;
+        is_valid = false;
+      }
+    }
+
+    if is_valid {
+      valid_tickets.push(ticket.clone());
+    }
+  }
+
+  println!("{}", error_sum);
+
+  let mut possibilities: Vec<BTreeSet<String>> = Vec::new();
+  for _ in 0 .. player_ticket.len() {
+    let mut all_fields = BTreeSet::new();
+    for field_name in rules.keys() {
+      all_fields.insert(field_name.clone());
+    }
+    possibilities.push(all_fields);
+  }
+
+  for ticket in valid_tickets {
+    //println!("{:?}", possibilities);
+    for i in 0 .. ticket.len() {
+      let mut fields_to_remove = Vec::new();
+
+      for field_name in possibilities[i].iter() {
+        let rule = rules.get(field_name).unwrap();
+        if !value_obeys_rule(ticket[i], rule) {
+          /*
+          println!("{}: value {} does not obey rule for {}",
+                   i, ticket[i], field_name);
+                   */
+          fields_to_remove.push(field_name.clone());
+        }
+      }
+
+      for field_name in fields_to_remove {
+        possibilities[i].remove(&field_name);
+      }
+    }
+  }
+
+  //println!("{:?}", possibilities);
+
+  let mut finalized_fields = BTreeSet::new();
+  loop {
+    let mut removed_any = false;
+
+    for i in 0 .. player_ticket.len() {
+      let mut unique_field = None;
+      if possibilities[i].len() == 1 {
+        let field_name = possibilities[i].iter().next().unwrap().clone();
+        if finalized_fields.contains(&field_name) {
+          continue;
+        }
+        unique_field = Some((i, field_name));
+      }
+
+      match unique_field {
+        Some((i_to_skip, field_name)) => {
+          removed_any = true;
+
+          for j in 0 .. possibilities.len() {
+            if j == i_to_skip {
+              continue;
+            }
+
+            possibilities[j].remove(&field_name);
+          }
+
+          finalized_fields.insert(field_name);
+        },
+        None => { },
+      }
+    }
+
+    if !removed_any {
+      break;
+    }
+  }
+
+  let mut product = 1;
+  for i in 0 .. possibilities.len() {
+    let field_name = possibilities[i].iter().next().unwrap();
+    if field_name.starts_with("departure ") {
+      product *= player_ticket[i];
+    }
+  }
+
+  println!("{}", product);
+
+  Ok(())
+}
+
+
+fn parse_comma_separated_ints(line: &str) -> Vec<i64> {
+  let mut result = Vec::new();
+
+  for word in line.split(',') {
+    result.push(word.parse::<i64>().unwrap());
+  }
+
+  result
+}
+
+
+fn value_obeys_rule(value: i64, rule: &Vec<Range>) -> bool {
+  for range in rule {
+    if value >= range.min && value <= range.max {
+      return true;
+    }
+  }
+  false
+}
+