2025 Day 9

Author: hsaikia

src/bin/2025_09/main.rs

@@ -0,0 +1,88 @@
+use std::collections::HashSet;
+
+use aoc::{common, io};
+
+fn intersect_inner(boundary: &[&(usize, usize)], p1: &(usize, usize), p2: &(usize, usize)) -> bool {
+    boundary
+        .iter()
+        .any(|b| b.0 > p1.0 && b.0 < p2.0 && b.1 > p1.1 && b.1 < p2.1)
+}
+
+fn solve<const PART: usize>(input: &str) -> usize {
+    let mut corner_pts = Vec::new();
+
+    for line in input.lines() {
+        if line.is_empty() {
+            continue;
+        }
+        let corners = io::tokenize_nums::<usize>(line, ",");
+        corner_pts.push(corners);
+    }
+
+    let mut boundary: HashSet<(usize, usize)> = HashSet::new();
+    for i in 0..corner_pts.len() {
+        for j in i + 1..corner_pts.len() {
+            if corner_pts[i][0] == corner_pts[j][0] {
+                let y1 = corner_pts[i][1].min(corner_pts[j][1]);
+                let y2 = corner_pts[i][1].max(corner_pts[j][1]);
+                for y in y1..=y2 {
+                    boundary.insert((corner_pts[i][0], y));
+                }
+            }
+
+            if corner_pts[i][1] == corner_pts[j][1] {
+                let x1 = corner_pts[i][0].min(corner_pts[j][0]);
+                let x2 = corner_pts[i][0].max(corner_pts[j][0]);
+                for x in x1..=x2 {
+                    boundary.insert((x, corner_pts[i][1]));
+                }
+            }
+        }
+    }
+
+    let boundary_vec: Vec<&(usize, usize)> = boundary.iter().collect();
+
+    let mut max_area = 0;
+    for i in 0..corner_pts.len() {
+        for j in i + 1..corner_pts.len() {
+            let xmin = corner_pts[i][0].min(corner_pts[j][0]);
+            let xmax = corner_pts[i][0].max(corner_pts[j][0]);
+            let ymin = corner_pts[i][1].min(corner_pts[j][1]);
+            let ymax = corner_pts[i][1].max(corner_pts[j][1]);
+            let x = xmax - xmin + 1;
+            let y = ymax - ymin + 1;
+
+            if x * y <= max_area {
+                continue;
+            }
+
+            if PART == 1 {
+                max_area = max_area.max(x * y);
+            } else if !intersect_inner(&boundary_vec, &(xmin, ymin), &(xmax, ymax)) {
+                //println!("{:?} {:?} => {}", corner_pts[i], corner_pts[j], x * y);
+                max_area = max_area.max(x * y);
+            }
+        }
+    }
+
+    max_area
+}
+
+fn main() {
+    if let Some(input) = common::get_input() {
+        common::timed(&input, solve::<1>, true);
+        common::timed(&input, solve::<2>, false);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_samples() {
+        let sample_input = "7,1\n11,1\n11,7\n9,7\n9,5\n2,5\n2,3\n7,3";
+        assert_eq!(solve::<1>(sample_input), 50);
+        assert_eq!(solve::<2>(sample_input), 24);
+    }
+}