don't re-parse every time

day06/src/main.rs

@@ -6,7 +6,7 @@ use std::{
 use winnow::{
     PResult, Parser,
     ascii::{newline, till_line_ending},
-    combinator::{alt, repeat, separated},
+    combinator::{alt, opt, repeat, separated},
 };
 
 fn main() {
@@ -36,8 +36,9 @@ fn pt2(input: &str) -> usize {
         }
     }
 
+    let board = Board::new(input);
     for loc in trace {
-        board = Board::new(input);
+        let mut board = board.clone();
         let mut steps = HashSet::new();
         board.set(loc, Cell::Obstacle);
         steps.insert(board.guard);
@@ -230,10 +231,10 @@ fn parse(input: &str) -> PResult<Board> {
     let mut gdir = Dir::N;
     let mut loc = Loc(0, 0);
 
-    let mut input = input;
-    let cells: Vec<Vec<Cell>> = separated(1.., parse_line, newline)
-        .parse_next(&mut input)
-        .unwrap();
+    let (cells, _): (Vec<Vec<Cell>>, _) =
+        winnow::combinator::seq!(separated(1.., parse_line, newline), opt(newline))
+            .parse(input)
+            .unwrap();
 
     for (row, line) in cells.iter().enumerate() {
         for (col, cell) in line.iter().enumerate() {