stuff

2024/Cargo.toml

@@ -5,6 +5,9 @@ members = ["day*"]
 [profile.release]
 debug = 1
 
+[profile.dev]
+opt-level = 1
+
 [workspace.dependencies]
 helper = { path = "../helper" }
 nom = "7.1.3"

2024/day06/src/lib.rs

@@ -12,7 +12,7 @@ helper::define_variants! {
         basic => crate::part1;
     }
     part2 {
-        basic => crate::part2;
+        brute_force => crate::part2, sample_count=2;
     }
 }
 
@@ -27,6 +27,14 @@ impl Day for Day06 {
 }
 
 fn part1(input: &str) -> u64 {
+    #[repr(u8)]
+    enum GuardState {
+        Up,
+        Down,
+        Left,
+        Right,
+    }
+
     let input = input.as_bytes();
 
     let width = input.iter().position(|&byte| byte == b'\n').unwrap() + 1; // account for newline
@@ -34,19 +42,25 @@ fn part1(input: &str) -> u64 {
         .iter()
         .position(|&byte| byte == b'^' || byte == b'>' || byte == b'<' || byte == b'v')
         .unwrap();
-    let mut guard_state = input[guard_pos];
+    let mut guard_state = match input[guard_pos] {
+        b'^' => GuardState::Up,
+        b'v' => GuardState::Down,
+        b'<' => GuardState::Left,
+        b'>' => GuardState::Right,
+        _ => unreachable!(),
+    };
 
     let mut reached_tiles = vec![false; input.len()];
     reached_tiles[guard_pos] = true;
 
     loop {
         let new_pos = match guard_state {
-            b'^' => guard_pos.checked_sub(width),
-            b'v' => guard_pos.checked_add(width),
-            b'<' => guard_pos.checked_sub(1),
-            b'>' => guard_pos.checked_add(1),
-            _ => unreachable!(),
+            GuardState::Up => guard_pos.checked_sub(width),
+            GuardState::Down => guard_pos.checked_add(width),
+            GuardState::Left => guard_pos.checked_sub(1),
+            GuardState::Right => guard_pos.checked_add(1),
         };
+
         match new_pos {
             None => {
                 break;
@@ -60,11 +74,10 @@ fn part1(input: &str) -> u64 {
             Some(new_pos) => {
                 if input[new_pos] == b'#' {
                     guard_state = match guard_state {
-                        b'^' => b'>',
-                        b'v' => b'<',
-                        b'<' => b'^',
-                        b'>' => b'v',
-                        _ => unreachable!(),
+                        GuardState::Up => GuardState::Right,
+                        GuardState::Down => GuardState::Left,
+                        GuardState::Left => GuardState::Up,
+                        GuardState::Right => GuardState::Down,
                     }
                 } else {
                     reached_tiles[new_pos] = true;
@@ -77,8 +90,94 @@ fn part1(input: &str) -> u64 {
     reached_tiles.iter().filter(|reached| **reached).count() as u64
 }
 
-fn part2(_input: &str) -> u64 {
-    0
+fn part2(input: &str) -> u64 {
+    #[derive(Clone, Copy)]
+    #[repr(u8)]
+    enum GuardState {
+        Up,
+        Down,
+        Left,
+        Right,
+    }
+
+    let input = input.as_bytes();
+
+    fn check_if_stuck(input: &[u8], mut guard_pos: usize, width: usize) -> bool {
+        let mut guard_state = match input[guard_pos] {
+            b'^' => GuardState::Up,
+            b'v' => GuardState::Down,
+            b'<' => GuardState::Left,
+            b'>' => GuardState::Right,
+            _ => unreachable!(),
+        };
+
+        let mut reached_tiles = vec![false; input.len() * 4];
+        let idx_reached =
+            |guard_pos: usize, guard_state: GuardState| (guard_pos << 2) | guard_state as usize;
+
+        loop {
+            if reached_tiles[idx_reached(guard_pos, guard_state)] {
+                return true;
+            }
+            reached_tiles[idx_reached(guard_pos, guard_state)] = true;
+
+            let new_pos = match guard_state {
+                GuardState::Up => guard_pos.checked_sub(width),
+                GuardState::Down => guard_pos.checked_add(width),
+                GuardState::Left => guard_pos.checked_sub(1),
+                GuardState::Right => guard_pos.checked_add(1),
+            };
+            match new_pos {
+                None => {
+                    break;
+                }
+                Some(new_pos) if input.len() <= new_pos => {
+                    break;
+                }
+                Some(new_pos) if input[new_pos] == b'\n' => {
+                    break;
+                }
+                Some(new_pos) => {
+                    if input[new_pos] == b'#' {
+                        guard_state = match guard_state {
+                            GuardState::Up => GuardState::Right,
+                            GuardState::Down => GuardState::Left,
+                            GuardState::Left => GuardState::Up,
+                            GuardState::Right => GuardState::Down,
+                        };
+                    } else {
+                        guard_pos = new_pos;
+                    }
+                }
+            }
+        }
+
+        false
+    }
+
+    let initial_guard_pos = input
+        .iter()
+        .position(|&byte| byte == b'^' || byte == b'>' || byte == b'<' || byte == b'v')
+        .unwrap();
+    let width = input.iter().position(|&byte| byte == b'\n').unwrap() + 1; // account for newline
+
+    let mut count = 0;
+    let mut modified_input = input.to_owned();
+    for i in 0..input.len() {
+        if input[i] == b'\n' || input[i] == b'#' || i == initial_guard_pos {
+            continue;
+        }
+        let prev = modified_input[i];
+
+        modified_input[i] = b'#';
+        if check_if_stuck(&modified_input, initial_guard_pos, width) {
+            count += 1;
+        }
+
+        modified_input[i] = prev;
+    }
+
+    count
 }
 
 helper::tests! {
@@ -88,8 +187,8 @@ helper::tests! {
         default => 4454;
     }
     part2 {
-        small => 0;
-        default => 0;
+        small => 6;
+        default => 1503;
     }
 }
 helper::benchmarks! {}