day 6 pt2

src/bin/05.rs

@@ -134,7 +134,6 @@ mod tests {
     }
 
     #[test]
-    #[ignore]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
         assert_eq!(result, Some(123));

src/bin/06.rs

@@ -1,7 +1,15 @@
+use std::collections::HashSet;
 use itertools::Itertools;
 
 advent_of_code::solution!(6);
 
+#[derive(PartialEq, Clone)]
+enum Tile {
+    Empty,
+    Object,
+    Guard
+}
+
 pub fn part_one(input: &str) -> Option<u32> {
     let mut pos = (0_isize, 0_isize);
     let mut dir = (-1_isize, 0_isize);
@@ -51,14 +59,127 @@ pub fn part_one(input: &str) -> Option<u32> {
     Some(count_spaces(visited) as u32)
 }
 
-pub fn part_two(_input: &str) -> Option<u32> {
-    None
+pub fn part_two(input: &str) -> Option<u32> {
+    let grid = input.lines().map(|line| line.chars().map(|c| {
+        match c {
+            '.' => Tile::Empty,
+            '#' => Tile::Object,
+            '^' => Tile::Guard,
+            _ => panic!()
+        }
+    }).collect_vec()).collect_vec();
+
+    let mut looper_count = 0;
+    // find all the spots the guard normally follows
+    // then see if placing an object on one of those spots creates a loop
+
+    let paths =  walk_path(&grid);
+    // println!("CHECKING {:?} PATHS", paths.len());
+
+    for (row_idx, col_idx) in paths {
+        if grid[row_idx][col_idx] != Tile::Empty { continue }
+        let mut test_grid = grid.clone();
+        test_grid[row_idx][col_idx] = Tile::Object; // Add a wall and check if it creates a loop
+
+        if does_loop(&test_grid) {
+            looper_count += 1;
+            // print!("!");
+            // let _ = io::stdout().flush();
+        } else {
+            // print!("x");
+            // let _ = io::stdout().flush();
+        }
+    }
+
+    Some(looper_count)
 }
 
 fn count_spaces(grid: Vec<Vec<i32>>) -> usize {
     grid.iter().flat_map(|line: &Vec<_>| line.iter().filter(|v| v > &&0)).count()
 }
 
+fn walk_path(grid: &Vec<Vec<Tile>>) -> Vec<(usize, usize)> {
+    let mut pos = grid.iter().enumerate().find_map(|(row_idx, row)| {
+        row.iter().enumerate().find_map(|(col_idx, cell)| {
+            if *cell == Tile::Guard { Some((row_idx as isize, col_idx as isize)) } else { None }
+        })
+    }).unwrap();
+    let mut dir = (-1_isize, 0_isize);
+
+    let mut history = HashSet::new();
+    history.insert((pos.0 as usize, pos.1 as usize));
+
+    let is_valid_position = |(row_idx, col_idx)| {
+        (0..grid.len() as isize).contains(&row_idx) && (0..grid[0].len() as isize).contains(&col_idx)
+    };
+
+    loop {
+        let new_pos = (pos.0 + dir.0, pos.1 + dir.1);
+        if !is_valid_position(new_pos) { break }
+
+        if grid[new_pos.0 as usize][new_pos.1 as usize] == Tile::Object {
+            // if it is a blocker, turn 90deg
+            let directions = [(-1, 0), (0, 1), (1, 0), (0, -1), (-1, 0)];
+            let new_dir = *directions.iter().skip_while(|d| **d != dir).nth(1).unwrap();
+            dir.0 = new_dir.0;
+            dir.1 = new_dir.1;
+        } else {
+            // else move into the new position and mark it as entered
+            history.insert((new_pos.0 as usize, new_pos.1 as usize));
+            pos.0 = new_pos.0;
+            pos.1 = new_pos.1;
+        }
+    }
+
+    history.into_iter().collect_vec()
+}
+
+fn does_loop(grid: &Vec<Vec<Tile>>) -> bool {
+    let mut pos = grid.iter().enumerate().find_map(|(row_idx, row)| {
+        row.iter().enumerate().find_map(|(col_idx, cell)| {
+            if *cell == Tile::Guard { Some((row_idx as isize, col_idx as isize)) } else { None }
+        })
+    }).unwrap();
+    let mut dir = (-1_isize, 0_isize);
+
+    let mut history = vec![];
+    history.push(((pos.0, pos.1), (-1_isize, 0_isize)));
+
+
+    let is_valid_position = |(row_idx, col_idx)| {
+        (0..grid.len() as isize).contains(&row_idx) && (0..grid[0].len() as isize).contains(&col_idx)
+    };
+
+    loop {
+        let new_pos = (pos.0 + dir.0, pos.1 + dir.1);
+        if !is_valid_position(new_pos) {
+            return false;
+        }
+
+        if grid[new_pos.0 as usize][new_pos.1 as usize] == Tile::Object {
+            // if it is a blocker, turn 90deg
+            let directions = [(-1, 0), (0, 1), (1, 0), (0, -1), (-1, 0)];
+            let new_dir = *directions.iter().skip_while(|d| **d != dir).nth(1).unwrap();
+
+            if history.contains(&(pos, new_dir)) {
+                return true;
+            }
+
+            dir.0 = new_dir.0;
+            dir.1 = new_dir.1;
+        } else {
+            // else move into the new position and mark it as entered
+            if history.contains(&((new_pos.0, new_pos.1), dir)) {
+                return true;
+            }
+
+            history.push(((new_pos.0, new_pos.1), dir));
+            pos.0 = new_pos.0;
+            pos.1 = new_pos.1;
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -81,7 +202,6 @@ mod tests {
     }
 
     #[test]
-    #[ignore]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
         assert_eq!(result, Some(6));

src/bin/13.rs

@@ -124,6 +124,7 @@ mod tests {
     }
 
     #[test]
+    #[ignore]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
         assert_eq!(result, Some(3440247820));

src/bin/16.rs

@@ -124,7 +124,7 @@ mod tests {
 
     #[test]
     fn test_part_one_2() {
-        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        let result = part_one(&advent_of_code::template::read_file_part("examples", DAY, 2));
         assert_eq!(result, Some(11048));
     }