Finished aoc day 15 part 1

advent_of_code/2022/15/src/main.rs

@@ -0,0 +1,98 @@
+use std::{collections::HashSet, hash::Hash};
+use nom::{
+    IResult,
+    character::complete::{self,multispace1},
+    multi::separated_list1, 
+    sequence::{preceded, separated_pair}, bytes::streaming::tag,
+};
+
+fn parse_input(input: &str) -> IResult<&str, Vec<((i32, i32), (i32, i32))>> {
+    let (input, coords) = separated_list1(
+        multispace1, 
+        preceded(
+            tag("Sensor at x="),
+            separated_pair(
+                separated_pair(
+                    complete::i32,
+                    tag(", y="),
+                    complete::i32,
+                ), 
+                tag(": closest beacon is at x="), 
+                separated_pair(
+                    complete::i32,
+                    tag(", y="),
+                    complete::i32,
+                ))
+            )
+        )(input)?;
+
+    Ok((input, coords))
+}
+
+fn manhattan_dist(a: (i32, i32), b: (i32, i32)) -> i32 {
+    return (a.0 - b.0).abs() + (a.1 - b.1).abs();
+}
+
+fn fill_map(beacon_map: &mut HashSet<(i32, i32)>, sensor_coord: (i32, i32), beacon_coord: (i32, i32)) {
+    let dist = manhattan_dist(sensor_coord, beacon_coord);
+    let (sx, sy) = sensor_coord;
+
+    for i in 0..=dist {
+        for j in 0..=i {
+            beacon_map.insert((sx + i, sy + j));
+            beacon_map.insert((sx - i, sy + j));
+            beacon_map.insert((sx + i, sy - j));
+            beacon_map.insert((sx - i, sy - j));
+        }
+    }
+}
+
+fn fill_line(beacon_line: &mut HashSet<i32>, sensor_coord: (i32, i32), beacon_coord: (i32, i32), test_line: i32) {
+    let dist = manhattan_dist(sensor_coord, beacon_coord);
+    let (sx, sy) = sensor_coord;
+
+    let cross_section_len = dist - (test_line - sy).abs();
+    if cross_section_len >= 0 {
+        for i in 0..=cross_section_len {
+            beacon_line.insert(sx + i);
+            beacon_line.insert(sx - i);
+        }
+    }
+}
+
+fn main() {
+    let test_y = 2000000;
+
+    let input_text = include_str!("../input.txt");
+    let (_rest, coord_list) = parse_input(input_text).unwrap();
+
+    // Testing the parsing
+
+    // for ((sx, sy), (bx, by)) in coord_list {
+    //     println!("Sensor at x={sx}, y={sy}: closest beacon is at x={bx}, y={by}");
+    // }
+
+
+    // Naive method
+
+    // let mut beacon_map = HashSet::new();
+
+    // for (sensor, beacon) in coord_list {
+    //     fill_map(&mut beacon_map, sensor, beacon);
+    // }
+
+    // let positions = beacon_map.into_iter().filter(|(_, y)| *y == test_y).count();
+
+    // println!("Number of positions with y={test_y}: {positions}");
+
+
+    // A slightly less naive approach
+
+    let mut beacon_line = HashSet::new();
+
+    for (sensor, beacon) in coord_list {
+        fill_line(&mut beacon_line, sensor, beacon, test_y);
+    }
+
+    println!("Number of positions with y={test_y}: {}", beacon_line.len() - 1);
+}