Day one

day-01-rust/src/task2.rs

@@ -0,0 +1,31 @@
+use std::collections::HashMap;
+use std::str::FromStr;
+
+pub fn run(input: &str) {
+    let mut first = Vec::<i64>::new();
+    let mut second = Vec::<i64>::new();
+    for line in input.split('\n') {
+        if let Some((first_part, second_part)) = line.split_once("   ") {
+            match i64::from_str(first_part) {
+                Ok(n) => first.push(n),
+                Err(err) => {
+                    eprintln!("Failed to parse first number from {}: {}", first_part, err);
+                }
+            }
+            match i64::from_str(second_part) {
+                Ok(n) => second.push(n),
+                Err(err) => {
+                    eprintln!("Failed to parse second number from {}: {}", second_part, err);
+                }
+            }
+        }
+    }
+
+    let mut second_counts = HashMap::<i64, i64>::new();
+    for element in second {
+        *second_counts.entry(element).or_insert(0) += 1;
+    }
+    
+    let result = first.iter().map(|num| num * second_counts.get(num).unwrap_or(&0)).sum::<i64>();
+    println!("Similarity: {}", result);
+}