Add Day 4 solution

rust/Cargo.toml

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+regex = "1"

rust/src/day4.rs

@@ -0,0 +1,60 @@
+use std::fs::File;
+use std::io::BufRead;
+use std::io::BufReader;
+
+use regex::Regex;
+
+#[derive(Debug, PartialEq, Eq)]
+struct ElfAssignment {
+    first_range_start: u8,
+    first_range_end: u8,
+    second_range_start: u8,
+    second_range_end: u8,
+}
+
+pub fn run() {
+    let file = File::open("resources/day4input.txt").expect("Input file not found.");
+    let reader = BufReader::new(file);
+
+    let re = Regex::new(r"^(\d{1,2})-(\d{1,2}),(\d{1,2})-(\d{1,2})$").unwrap();
+    let assignments: Vec<Option<ElfAssignment>> = reader
+        .lines()
+        .map(|line| {
+            let unwrapped_line = line.unwrap();
+            let cap = re.captures(unwrapped_line.as_str()).unwrap();
+            let groups = (cap.get(1), cap.get(2), cap.get(3), cap.get(4));
+            match groups {
+                (Some(r1), Some(r2), Some(r3), Some(r4)) => Some(ElfAssignment {
+                    first_range_start: r1.as_str().parse::<u8>().unwrap(),
+                    first_range_end: r2.as_str().parse::<u8>().unwrap(),
+                    second_range_start: r3.as_str().parse::<u8>().unwrap(),
+                    second_range_end: r4.as_str().parse::<u8>().unwrap(),
+                }),
+                _ => None,
+            }
+        })
+        .collect();
+
+    let mut total_overlap: u32 = 0;
+    let mut partial_overlap: u32 = 0;
+
+    for assignment in assignments {
+        let a = assignment.unwrap();
+        if (a.first_range_start >= a.second_range_start
+            && a.first_range_end <= a.second_range_end) ||
+            (a.second_range_start >= a.first_range_start
+                && a.second_range_end <= a.first_range_end) {
+            total_overlap += 1;
+        }
+
+        if ((a.first_range_start >= a.second_range_start && a.first_range_start <= a.second_range_end) ||
+            (a.first_range_end >= a.second_range_start && a.first_range_end <= a.second_range_end)) ||
+            ((a.second_range_start >= a.first_range_start && a.second_range_start <= a.first_range_end) ||
+                (a.second_range_end >= a.first_range_start && a.second_range_end <= a.first_range_end)) {
+            partial_overlap += 1;
+        }
+    }
+
+    println!("Day 4 Answer 1: {:?}", total_overlap);
+    println!("Day 4 Answer 2: {:?}", partial_overlap);
+}

rust/src/main.rs

@@ -3,6 +3,7 @@ use std::env;
 mod day1;
 mod day2;
 mod day3;
+mod day4;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
@@ -13,6 +14,7 @@ fn main() {
                 "day1" => day1::run(),
                 "day2" => day2::run(),
                 "day3" => day3::run(),
+                "day4" => day4::run(),
                 _ => eprintln!("error: invalid day")
             }
         },