From 33b3d303a0d3d6c91f390811a8e355bbe5d83928 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Thu, 2 Dec 2021 00:48:01 -0500
Subject: [PATCH] Avoid unneeded heap allocation in day 2

---
 day2/src/main.rs | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/day2/src/main.rs b/day2/src/main.rs
index 99d963c..dee8949 100644
--- a/day2/src/main.rs
+++ b/day2/src/main.rs
@@ -113,18 +113,21 @@ fn parse_line(line: &str) -> IResult<&str, Direction> {
 fn main() {
     let input_file_name = env::args().nth(1).expect("No input filename specified");
     let input_file = File::open(input_file_name).expect("Could not open input file");
-    let lines = BufReader::new(input_file)
+    let directions = BufReader::new(input_file)
         .lines()
         .map(|res| res.expect("Failed to read line"))
-        .collect::<Vec<_>>();
-
-    let directions = lines
-        .iter()
         .map(|line| {
-            parse_line(line)
-                .unwrap_or_else(|err| panic!("Failed to parse line '{}': {}", line, err))
+            let (remaining, direction) = parse_line(&line)
+                .unwrap_or_else(|err| panic!("Failed to parse line '{}': {}", line, err));
+
+            assert!(
+                remaining.is_empty(),
+                "Input remained after parsing: {}",
+                remaining
+            );
+
+            direction
         })
-        .map(|(_, direction)| direction)
         .collect::<Vec<_>>();
 
     println!("Part 1: {}", simulate(&directions, &Part::Part1));