add day 8

2022/Cargo.toml

@@ -35,6 +35,10 @@ path = "src/day6.rs"
 name = "day7"
 path = "src/day7.rs"
 
+[[bin]]
+name = "day8"
+path = "src/day8.rs"
+
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]

2022/src/day8.rs

@@ -0,0 +1,93 @@
+const DATA: &'static str = include_str!("../data/day8.txt");
+// const DATA: &'static str = "
+// 30373
+// 25512
+// 65332
+// 33549
+// 35390
+// ";
+
+
+// O(N * (2 * sqrt(N) - 1)), so roughly N^1.5? Where N is number of elements in the grid
+fn is_visible(grid: &Vec<Vec<usize>>, x: usize, y: usize) -> bool {
+    let height = grid[y][x];
+    let rows = grid.len();
+    let cols = grid[x].len();
+    // search horizontal
+    let vis_left = (0..x).all(|cmp_x| grid[y][cmp_x] < height);
+    let vis_right = ((x + 1)..cols).all(|cmp_x| grid[y][cmp_x] < height);
+
+    let vis_top = (0..y).all(|cmp_y| grid[cmp_y][x] < height);
+    let vis_bottom = ((y + 1)..rows).all(|cmp_y| grid[cmp_y][x] < height);
+
+    vis_left || vis_right || vis_top || vis_bottom
+}
+
+
+fn scenic_score(grid: &Vec<Vec<usize>>, x: usize, y: usize) -> usize {
+    let height = grid[y][x];
+    let rows = grid.len();
+    let cols = grid[x].len();
+
+    let sc_left = (0..x).rev()
+        .position(|cmp_x| grid[y][cmp_x] >= height) // 0-indexed position of the first blocking tree
+        .map(|p| p + 1) // +1 since we include the blocking tree in the count
+        .unwrap_or(x); // if no blocking trees, score is how many are to the left of current
+
+    let sc_right = ((x + 1)..cols)
+        .position(|cmp_x| grid[y][cmp_x] >= height)
+        .map(|p| p + 1)
+        .unwrap_or(cols - x - 1); // e.g. if x is 4 and there are 5 cols, this is rightmost, so 5 - 4 - 1 = 0
+
+    let sc_top = (0..y).rev()
+        .position(|cmp_y| grid[cmp_y][x] >= height)
+        .map(|p| p + 1)
+        .unwrap_or(y);
+
+    let sc_bottom = ((y + 1)..rows)
+        .position(|cmp_y| grid[cmp_y][x] >= height)
+        .map(|p| p + 1)
+        .unwrap_or(rows - y - 1);
+
+    sc_left * sc_right * sc_top * sc_bottom
+}
+
+
+fn build_grid(data: &str) -> Result<Vec<Vec<usize>>, String> {
+    data.trim()
+        .lines()
+        .map(|line| {
+            line.chars()
+                .map(|c| c.to_digit(10).map(|c| c as usize).ok_or_else(|| format!("Failed to convert to integer: {c}") ))
+                .collect::<Result<Vec<usize>, String>>()
+        })
+        .collect::<Result<Vec<Vec<usize>>, String>>()
+}
+
+
+fn main() -> Result<(), String> {
+    let grid = build_grid(DATA)?;
+
+    let mut visible_trees = 0;
+    for y in 0..grid.len() {
+        for x in 0..grid[y].len() {
+            if is_visible(&grid, x, y) {
+                visible_trees += 1;
+            }
+        }
+    }
+    println!("Part 1: {visible_trees}");
+
+    let mut max_score = 0;
+    for y in 0..grid.len() {
+        for x in 0..grid[y].len() {
+            let score = scenic_score(&grid, x, y);
+            if score > max_score {
+                max_score = score;
+            }
+        }
+    }
+    println!("Part 2: {max_score}");
+
+    Ok(())
+}