add: day 8

data/examples/08.txt

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+25512
+65332
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src/bin/08.rs

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+use itertools::Itertools;
+use std::collections::HashSet;
+
+advent_of_code::solution!(8);
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let grid = Grid::new(input);
+    let ans = grid.count_all_visibles();
+
+    Some(ans)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let grid = Grid::new(input);
+    let ans = grid.get_best_visibility();
+
+    Some(ans)
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct Pos(usize, usize);
+
+#[derive(Debug)]
+struct Grid {
+    grid: Vec<Vec<u32>>,
+    m: usize,
+    n: usize,
+}
+
+impl Grid {
+    fn new(input: &str) -> Self {
+        let grid = input
+            .lines()
+            .map(|line| line.chars().map(|c| c.to_digit(10).unwrap()).collect_vec())
+            .collect_vec();
+        let (m, n) = (grid.len(), grid[0].len());
+
+        Self { grid, m, n }
+    }
+
+    fn get_val(&self, pos: &Pos) -> u32 {
+        self.grid[pos.0][pos.1]
+    }
+
+    fn get_new_pos(&self, pos: Pos, delta: (isize, isize)) -> Option<Pos> {
+        let i = pos.0.checked_add_signed(delta.0)?;
+        let j = pos.1.checked_add_signed(delta.1)?;
+
+        (self.m > i && self.n > j).then_some(Pos(i, j))
+    }
+
+    fn _get_visible_pos_in_a_direction(&self, mut pos: Pos, delta: (isize, isize)) -> Vec<Pos> {
+        let mut visible_pos = vec![pos];
+
+        while let Some(new_pos) = self.get_new_pos(pos, delta) {
+            pos = new_pos;
+
+            if let Some(last) = visible_pos.last() {
+                if self.get_val(last) >= self.get_val(&new_pos) {
+                    continue;
+                }
+            }
+            visible_pos.push(new_pos);
+        }
+
+        visible_pos
+    }
+
+    fn count_all_visibles(&self) -> u32 {
+        let mut visible_pos = HashSet::new();
+
+        for i in 0..self.m {
+            visible_pos.extend(self._get_visible_pos_in_a_direction(Pos(i, 0), (0, 1)));
+            visible_pos.extend(self._get_visible_pos_in_a_direction(Pos(i, self.n - 1), (0, -1)));
+        }
+        for j in 0..self.n {
+            visible_pos.extend(self._get_visible_pos_in_a_direction(Pos(0, j), (1, 0)));
+            visible_pos.extend(self._get_visible_pos_in_a_direction(Pos(self.m - 1, j), (-1, 0)));
+        }
+
+        visible_pos.len() as u32
+    }
+
+    fn _update_visibility_in_a_direction(
+        &self,
+        mut pos: Pos,
+        delta: (isize, isize),
+        visibility: &mut Vec<Vec<u32>>,
+    ) {
+        let mut stack = vec![(u32::MAX, 0)];
+        let mut i = 0;
+
+        loop {
+            let height = self.get_val(&pos);
+            while stack.last().unwrap().0 < height {
+                stack.pop();
+            }
+
+            visibility[pos.0][pos.1] *= i - stack.last().unwrap().1;
+
+            stack.push((height, i));
+
+            if let Some(new_pos) = self.get_new_pos(pos, delta) {
+                pos = new_pos;
+                i += 1;
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn get_best_visibility(&self) -> u32 {
+        let mut visibility = vec![vec![1; self.n]; self.m];
+
+        for i in 0..self.m {
+            self._update_visibility_in_a_direction(Pos(i, 0), (0, 1), &mut visibility);
+            self._update_visibility_in_a_direction(Pos(i, self.n - 1), (0, -1), &mut visibility);
+        }
+        for j in 0..self.n {
+            self._update_visibility_in_a_direction(Pos(0, j), (1, 0), &mut visibility);
+            self._update_visibility_in_a_direction(Pos(self.m - 1, j), (-1, 0), &mut visibility);
+        }
+
+        *visibility.iter().flatten().max().unwrap()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(21));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(8));
+    }
+}