refactored project structure

src/day06/part06a.rs

@@ -0,0 +1,27 @@
+
+pub fn solve(puzzle: String) -> u64 {
+    let mut iters: Vec<_> = puzzle
+        .lines()
+        .map(|line| line.split_whitespace())
+        .collect();
+
+    std::iter::from_fn(move || {
+        let column: Option<Vec<&str>> = iters
+            .iter_mut()
+            .map(|it| it.next())
+            .collect::<Option<Vec<_>>>();
+
+        let column = column?;
+
+        Some((
+            column[..column.len() - 1].iter().map(|v| v.parse::<u64>().unwrap()).collect::<Vec<_>>(),
+            *column.last().unwrap(),
+        ))
+    }).map(|(vals, op)| {
+        match op {
+           "+" => vals.iter().sum::<u64>(),
+           "*" => vals.iter().product::<u64>(),
+           _ => unreachable!(),
+       }
+    }).sum::<u64>()
+}