day 12 pt 1

data/examples/12-2.txt

@@ -0,0 +1,5 @@
+OOOOO
+OXOXO
+OOOOO
+OXOXO
+OOOOO

data/examples/12-3.txt

@@ -0,0 +1,10 @@
+RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE

data/examples/12.txt

@@ -0,0 +1,4 @@
+AAAA
+BBCD
+BBCC
+EEEC

src/bin/12.rs

@@ -0,0 +1,134 @@
+use itertools::Itertools;
+use std::{collections::HashMap, fmt};
+
+advent_of_code::solution!(12);
+
+struct Plot {
+    letter: char,
+    region_id: Option<u32>,
+}
+impl fmt::Debug for Plot {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}{}", self.letter, self.region_id.unwrap_or(0))
+    }
+}
+
+#[derive(Debug)]
+struct Region {
+    edges: usize,
+    count: usize
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let mut plots = input.lines().map(|l| l.chars().map(|c| Plot { letter: c, region_id: None }).collect_vec()).collect_vec();
+    let mut regions: HashMap<u32, Region> = HashMap::new();
+    let mut next_region_id = 1;
+
+    while let Some(plot) = get_next_unassigned_plot(&plots) {
+        plots[plot.0][plot.1].region_id = Some(next_region_id);
+
+        let edge_count = count_edges(&plots, &plot);
+        regions.insert(next_region_id, Region { edges: edge_count, count: 1 });
+        next_region_id += 1;
+
+        update_neighbors(&mut plots, &plot, &mut regions);
+    }
+
+    // println!("{:?}", plots);
+    // println!("{:?}", regions);
+    let total = regions.into_iter().fold(0, |sum, (_key, region)| {
+        sum + (region.edges * region.count)
+    });
+
+    Some(total as u32)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    None
+}
+
+fn get_next_unassigned_plot(plots: &Vec<Vec<Plot>>) -> Option<(usize, usize)> {
+    for (row_idx, row) in plots.iter().enumerate() {
+        for (col_idx, plot) in row.iter().enumerate() {
+            if plot.region_id == None {
+                // println!("FOUND unassigned plot! ({}, {})", row_idx, col_idx);
+                return Some((row_idx, col_idx))
+            }
+        }
+    }
+    return None
+}
+
+fn update_neighbors(plots: &mut Vec<Vec<Plot>>, plot: &(usize, usize), regions: &mut HashMap<u32, Region>) {
+    let grid_height = plots.len();
+    let grid_width = plots[0].len();
+
+    let current_region_id = plots[plot.0][plot.1].region_id.unwrap();
+    let current_region_letter = plots[plot.0][plot.1].letter;
+
+    // println!("UPDATING plot ({}, {}) - {}:{}", plot.0, plot.1, current_region_letter, current_region_id.unwrap());
+
+    let directions: Vec<(isize, isize)> = vec![(-1, 0), (1, 0), (0, -1), (0, 1)];
+    for d in directions {
+        let new_row_idx = &(plot.0 as isize + d.0);
+        let new_col_idx = &(plot.1 as isize + d.1);
+        let should_update =
+            (0..grid_height as isize).contains(new_row_idx) &&
+            (0..grid_width as isize).contains(new_col_idx) &&
+            plots[*new_row_idx as usize][*new_col_idx as usize].letter == current_region_letter &&
+            plots[*new_row_idx as usize][*new_col_idx as usize].region_id == None;
+
+        if should_update {
+            let next_plot: (usize, usize) = (*new_row_idx as usize, *new_col_idx as usize);
+            plots[next_plot.0][next_plot.1].region_id = Some(current_region_id);
+            let region = regions.get_mut(&current_region_id).unwrap();
+            region.count += 1;
+            let new_edges = count_edges(plots, &next_plot);
+            region.edges += new_edges;
+
+            update_neighbors(plots, &next_plot, regions)
+        }
+    }
+}
+
+fn count_edges(plots: &Vec<Vec<Plot>>, plot: &(usize, usize)) -> usize {
+    let grid_height = plots.len();
+    let grid_width = plots[0].len();
+
+    vec![(-1, 0), (1, 0), (0, -1), (0, 1)].iter().filter(|d| {
+        let new_row = plot.0 as isize + &d.0;
+        let new_col = plot.1 as isize + &d.1;
+
+        !(0..grid_height as isize).contains(&new_row) ||
+        !(0..grid_width as isize).contains(&new_col) ||
+        plots[new_row as usize][new_col as usize].letter != plots[plot.0][plot.1].letter
+    }).count()
+}
+#[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(140));
+    }
+
+    #[test]
+    fn test_part_one_2() {
+        let result = part_one(&advent_of_code::template::read_file_part("examples", DAY, 2));
+        assert_eq!(result, Some(772));
+    }
+
+    #[test]
+    fn test_part_one_3() {
+        let result = part_one(&advent_of_code::template::read_file_part("examples", DAY, 3));
+        assert_eq!(result, Some(1930));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, None);
+    }
+}