day 10 pt 1

data/examples/10-2.txt

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

data/examples/10.txt

@@ -0,0 +1,4 @@
+0123
+1234
+8765
+9876

src/bin/10.rs

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+use itertools::Itertools;
+
+advent_of_code::solution!(10);
+
+#[derive(Debug)]
+#[derive(PartialEq)]
+struct Path {
+    row: isize,
+    col: isize,
+    elevation: u32,
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    // build the grid
+    let grid = input.lines().map(|line|
+        line.chars().map(|c| c.to_digit(10).unwrap() ).collect_vec()
+    ).collect_vec();
+
+    let peaks = grid.iter().enumerate().flat_map(|(row_idx, row)|
+        row.iter().enumerate().filter_map(move |(col_idx, c)|
+            if *c == 9 { Some(Path { row: row_idx as isize, col: col_idx as isize, elevation: 9 }) } else { None }
+        )
+    ).collect_vec();
+
+    // find the trailheads
+    let trailheads = grid.iter().enumerate().flat_map(|(row_idx, row)|
+        row.iter().enumerate().filter_map(move |(col_idx, c)|
+            if *c == 0 { Some(Path { row: row_idx as isize, col: col_idx as isize, elevation: 0 }) } else { None }
+        )
+    ).collect_vec();
+
+
+    let total_score = trailheads.iter().cartesian_product(&peaks).filter_map(|(trail, peak)| {
+        if can_navigate(&grid, trail, peak) { Some(true) } else { None }
+    }).count();
+
+    Some(total_score as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    None
+}
+
+const DIRECTIONS: &[(isize, isize); 4] = &[(-1,0), (1,0), (0,-1), (0,1)]; // UP, DOWN, LEFT, RIGHT
+
+fn can_navigate(grid: &Vec<Vec<u32>>, start: &Path, end: &Path) -> bool {
+    let grid_height = grid.len();
+    let grid_width = grid[0].len();
+    let is_valid = |p: &Path| (0..grid_height as isize).contains(&p.row) && (0..grid_width as isize).contains(&p.col) && grid[p.row as usize][p.col as usize] == p.elevation;
+
+    if start == end { return true }
+
+    DIRECTIONS.iter().any(|d| {
+        let next_step = Path { row: &start.row + d.0, col: &start.col + d.1, elevation: start.elevation + 1 };
+        // println!("{:?} ==> {:?} ?", start, end);
+        is_valid(&next_step) && can_navigate(&grid, &next_step, &end)
+    })
+}
+
+#[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(1));
+    }
+
+    #[test]
+    fn test_part_one_2() {
+        let result = part_one(&advent_of_code::template::read_file_part("examples", DAY, 2));
+        assert_eq!(result, Some(36));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}