Solve day 6

input/06-0.in

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input/06-1.in

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src/bin/06.rs

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+use std::collections::HashSet;
+
+static DIR_MAP: [(isize, isize); 4] = [(0, -1), (1, 0), (0, 1), (-1, 0)];
+
+fn find_loop(mut pos: (usize, usize), mut dir: usize, map: &[Vec<bool>]) -> bool {
+    let mut visited = HashSet::new();
+
+    visited.insert((pos, dir));
+
+    while let Some(next_pos) = Option::zip(
+        pos.0
+            .checked_add_signed(DIR_MAP[dir].0)
+            .filter(|&x| x < map[0].len()),
+        pos.1
+            .checked_add_signed(DIR_MAP[dir].1)
+            .filter(|&y| y < map[0].len()),
+    ) {
+        visited.insert((pos, dir));
+        if map[next_pos.1][next_pos.0] {
+            dir = (dir + 1) % 4;
+        } else {
+            pos = next_pos;
+        }
+        if visited.contains(&(pos, dir)) {
+            return true;
+        }
+    }
+
+    false
+}
+
+fn main() {
+    let text = std::fs::read_to_string("input/06-1.in").unwrap();
+
+    let mut start_pos = (0, 0);
+    let mut dir = 0;
+
+    let mut map = text
+        .lines()
+        .enumerate()
+        .map(|(y, l)| {
+            l.chars()
+                .enumerate()
+                .map(move |(x, c)| (x, y, c))
+                .map(|(x, y, c)| match c {
+                    '#' => true,
+                    '.' => false,
+                    '^' => {
+                        start_pos = (x, y);
+                        false
+                    }
+                    _ => unreachable!(),
+                })
+                .collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>();
+
+    let mut pos = start_pos;
+    let mut visited = HashSet::new();
+
+    visited.insert(pos);
+
+    while let Some(next_pos) = Option::zip(
+        pos.0
+            .checked_add_signed(DIR_MAP[dir].0)
+            .filter(|&x| x < map[0].len()),
+        pos.1
+            .checked_add_signed(DIR_MAP[dir].1)
+            .filter(|&y| y < map[0].len()),
+    ) {
+        if map[next_pos.1][next_pos.0] {
+            dir = (dir + 1) % 4;
+        } else {
+            pos = next_pos;
+            visited.insert(pos);
+        }
+    }
+
+    println!("{}", visited.len());
+
+    let mut count = 0;
+    for y in 0..map.len() {
+        for x in 0..map[0].len() {
+            if !map[y][x] {
+                map[y][x] = true;
+                if find_loop(start_pos, 0, &map) {
+                    count += 1;
+                }
+                map[y][x] = false;
+            }
+        }
+    }
+
+    println!("{}", count);
+}