Part 2 done

day_1/part2.rs

@@ -0,0 +1,43 @@
+use std::fs::File;
+use std::io::{self, BufRead};
+use std::path::Path;
+use std::collections::HashMap;
+use std::env;
+
+fn read_lines<P>(filename: P) -> io::Result<io::Lines<io::BufReader<File>>>
+where P: AsRef<Path>, {
+    let file = File::open(filename)?;
+    Ok(io::BufReader::new(file).lines())
+}
+
+fn main() {
+    let mut occurrences: HashMap<i32, i32> = HashMap::new();
+    let mut left_list: Vec<i32> = vec![];
+    let mut right_list: Vec<i32> = vec![];
+
+    let args: Vec<_> = env::args().collect();
+
+    if let Ok(lines) = read_lines(args[1].clone()) {
+        for line in lines.flatten() {
+            let parts = line.split("   ").collect::<Vec<_>>();
+            let lnum = parts[0].parse::<i32>().unwrap();
+            let rnum = parts[1].parse::<i32>().unwrap();
+            left_list.push(lnum);
+            right_list.push(rnum);
+        }
+        for left_n in left_list {
+            let entry = occurrences.entry(left_n).or_insert(0);
+            for right_n in &right_list {
+                if left_n == *right_n {
+                    *entry += 1;
+                }
+            }
+        }
+
+        let mut sum = 0;
+        for (num, count) in &occurrences {
+            sum += num * count;
+        }
+        println!("{}", sum)
+    }
+}