Day 2 part 1

src/day2.rs

@@ -0,0 +1,43 @@
+use std::error::Error;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::collections::HashMap;
+
+const INPUT: &str = "inputs/2.txt";
+
+pub fn solve() -> Result<usize, Box<Error>> {
+    calculate_checksum(INPUT)
+}
+
+fn calculate_checksum(filename: &str) -> Result<usize, Box<Error>> {
+    let mut two_count = 0;
+    let mut three_count = 0;
+    let file = File::open(filename)?;
+    for line in BufReader::new(file).lines() {
+        let mut char_map: HashMap<char, usize> = HashMap::new();
+        for c in line?.chars() {
+            let current_count = char_map.get(&c).unwrap_or(&0);
+            char_map.insert(c, current_count + 1);
+        }
+
+        if char_map.values().any(|&count| count == 2) {
+            two_count += 1
+        }
+        if char_map.values().any(|&count| count == 3) {
+            three_count += 1
+        }
+    }
+    Ok(two_count * three_count)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "inputs/2_test.txt";
+
+    #[test]
+    fn calculates_correct_checksum() {
+        assert_eq!(calculate_checksum(TEST_INPUT).unwrap(), 12);
+    }
+}