Day 10

1 files changed, 69 insertions, 0 deletions

diff --git a/day10/src/main.rs b/day10/src/main.rs
new file mode 100644
index 0000000..11f1f2c
--- /dev/null
+++ b/day10/src/main.rs
@@ -0,0 +1,69 @@
+use std::fs;
+use std::path::Path;
+use std::collections::HashMap;
+use lazy_static::lazy_static;
+
+lazy_static! {
+    static ref SCORE1: HashMap<u8,u32> = {
+        let mut m = HashMap::new();
+        m.insert(b')', 3);
+        m.insert(b']', 57);
+        m.insert(b'}', 1197);
+        m.insert(b'>', 25137);
+        m
+    };
+    static ref SCORE2: HashMap<u8,u64> = {
+        let mut m = HashMap::new();
+        m.insert(b')', 1);
+        m.insert(b']', 2);
+        m.insert(b'}', 3);
+        m.insert(b'>', 4);
+        m
+    };
+}
+
+/* AOC21 Day 10: https://adventofcode.com/2021/day/10 */
+fn main() {
+    let input = Path::new("resources").join("input.txt");
+    let content = fs::read_to_string(input).expect("Unable to read input file");
+    ex1(&content);
+    ex2(&content);
+}
+
+fn ex1(content: &str) {
+    let ex1: u32 =
+        content.lines()
+               .filter_map(|l| check_line(l).err())
+               .sum();
+    println!("Ex1: the result is {}", ex1);
+}
+
+fn ex2(content: &str) {
+    let mut ex2: Vec<u64> =
+        content.lines()
+               .filter_map(|l| check_line(l).ok())
+               .map(|v| v.iter().rev().fold(0, |a,p| a*5 + SCORE2.get(p).unwrap()))
+               .collect();
+    ex2.sort();
+    println!("Ex2: the result is {}", ex2[ex2.len()/2]);
+}
+
+fn check_line(line: &str) -> Result<Vec<u8>,u32> {
+    let acc = Ok(Vec::with_capacity(line.len()));
+    line.bytes().fold(acc, |a,c| match a {
+        Ok(mut a) => {
+            match c {
+                b'(' => { a.push(b')'); Ok(a) },
+                b'[' | b'{' | b'<' => { a.push(c+2); Ok(a) },
+                b')' | b']' | b'}' | b'>' => 
+                    if a.pop().filter(|&x| x == c).is_some() {
+                        Ok(a)
+                    } else {
+                        Err(*SCORE1.get(&c).unwrap())
+                    },
+                _ => unreachable!()
+            }
+        },
+        Err(_) => a
+    })
+}