star two

src/main.rs

@@ -1,11 +1,13 @@
 use std::env;
 
 mod star_one;
+mod star_two;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
     match args[1].as_str() {
         "1" => star_one::run(),
+        "2" => star_two::run(),
         _ => unreachable!(),
     }
 }

src/star_one.rs

@@ -82,4 +82,4 @@ mod tests {
         let result = calculate_total_distance(list_one, list_two);
         assert_eq!(result, 11);
     }
-}
+}

src/star_two.rs

@@ -0,0 +1,81 @@
+use std::collections::HashMap;
+
+use std::fs;
+
+pub fn run() {
+    let file = fs::read_to_string("./inputs/star_two.txt").unwrap();
+    let input = file.lines();
+    let parsed_input = parse_input(input);
+    let result = calculate_similarity_score(parsed_input.0, parsed_input.1);
+    println!("Result: {}", result);
+}
+
+fn parse_input<'a, I>(str_lines: I) -> (Vec<isize>, Vec<isize>)
+where
+    I: IntoIterator<Item = &'a str>
+{
+    let mut list_one = vec![];
+    let mut list_two = vec![];
+
+    for str_line in str_lines {
+        if str_line.trim().len() < 1 {
+            continue;
+        }
+        let mut elements = str_line.split_whitespace();
+        let val_one: isize = elements.next().unwrap().parse().unwrap();
+        let val_two: isize = elements.last().unwrap().parse().unwrap();
+        list_one.push(val_one);
+        list_two.push(val_two);
+    }
+
+    (list_one, list_two)
+}
+
+fn calculate_similarity_score(list_one: Vec<isize>, list_two: Vec<isize>) -> isize {
+    let mut result = 0;
+    let mut id_count = HashMap::new();
+
+    for id in list_two.iter() {
+        let current_count = id_count.entry(id).or_insert(0);
+        *current_count += 1;
+    }
+
+    for id in list_one.iter() {
+        let count = match id_count.get(id) {
+            Some(count) => *count,
+            None => 0,
+        };
+
+        result += *id * count;
+    }
+
+    result
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_parse_input() {
+        let input = vec![
+            "3   4",
+            "4   3",
+            "2   5",
+            "1   3",
+            "3   9",
+            "3   3",
+        ];
+        let result = parse_input(input);
+        assert_eq!(result, (vec![3, 4, 2, 1, 3, 3], vec![4, 3, 5, 3, 9, 3]));
+    }
+
+    #[test]
+    fn test_calculate_similarity_score() {
+        let list_one = vec![3, 4, 2, 1, 3, 3];
+        let list_two = vec![4, 3, 5, 3, 9, 3];
+        let result = calculate_similarity_score(list_one, list_two);
+        assert_eq!(result, 31);
+    }
+}