Day 10

src/bin/10.rs

@@ -0,0 +1,97 @@
+use std::collections::VecDeque;
+
+type Line = VecDeque<char>;
+
+fn main() {
+    let (score, incomplete_lines) = part1();
+    println!("First solution: {}", score);
+    println!("Second solution: {}", part2(incomplete_lines));
+}
+
+fn part1() -> (usize, Vec<Line>) {
+    let mut score = 0;
+
+    let mut input = input();
+    input.retain(|f| {
+        let mut stack = Vec::new();
+        let mut line = f.clone();
+        while let Some(next) = line.pop_front() {
+            if is_open(next) {
+                stack.push(next);
+            } else {
+                let popped = stack.pop().unwrap();
+                if !is_pair(popped, next) {
+                    // This line is corrupted.
+                    score += char_score_invalid(next);
+                    return false;
+                }
+            }
+        }
+        true
+    });
+
+    (score, input)
+}
+
+fn part2(lines: Vec<Line>) -> usize {
+    let mut scores = Vec::new();
+
+    for mut line in lines {
+        let mut stack = Vec::new();
+        while let Some(next) = line.pop_front() {
+            if is_open(next) {
+                stack.push(next);
+            } else {
+                stack.pop();
+            }
+        }
+
+        let mut score = 0;
+        while let Some(next) = stack.pop() {
+            score *= 5;
+            score += char_score_incomplete(next);
+        }
+        scores.push(score);
+    }
+
+    scores.sort_unstable();
+    scores[scores.len() / 2]
+}
+
+fn is_open(c: char) -> bool {
+    matches!(c, '<' | '{' | '[' | '(')
+}
+
+fn is_pair(open: char, close: char) -> bool {
+    matches!(
+        (open, close),
+        ('<', '>') | ('{', '}') | ('(', ')') | ('[', ']')
+    )
+}
+
+fn char_score_invalid(c: char) -> usize {
+    match c {
+        ')' => 3,
+        ']' => 57,
+        '}' => 1197,
+        '>' => 25137,
+        c => panic!("invalid char for score '{}'", c),
+    }
+}
+
+fn char_score_incomplete(c: char) -> usize {
+    match c {
+        '(' => 1,
+        '[' => 2,
+        '{' => 3,
+        '<' => 4,
+        c => panic!("invalid char for score '{}'", c),
+    }
+}
+
+fn input() -> Vec<Line> {
+    include_str!("../../input/10.txt")
+        .lines()
+        .map(|s| s.chars().collect())
+        .collect()
+}