Day 15. meh. it was alright

day15/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "aho-corasick"
+version = "0.7.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc936419f96fa211c1b9166887b38e5e40b19958e5b895be7c1f93adec7071ac"
+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "day15"
+version = "0.1.0"
+dependencies = [
+ "regex",
+]
+
+[[package]]
+name = "memchr"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+
+[[package]]
+name = "regex"
+version = "1.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e076559ef8e241f2ae3479e36f97bd5741c0330689e217ad51ce2c76808b868a"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.6.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "456c603be3e8d448b072f410900c09faf164fbce2d480456f50eea6e25f9c848"

day15/Cargo.toml

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+[package]
+name = "day15"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+regex = "1.7.0"

day15/data.txt

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+Sensor at x=2288642, y=2282562: closest beacon is at x=1581951, y=2271709
+Sensor at x=2215505, y=2975419: closest beacon is at x=2229474, y=3709584
+Sensor at x=275497, y=3166843: closest beacon is at x=-626874, y=3143870
+Sensor at x=1189444, y=2115305: closest beacon is at x=1581951, y=2271709
+Sensor at x=172215, y=2327851: closest beacon is at x=-101830, y=2000000
+Sensor at x=3953907, y=1957660: closest beacon is at x=2882446, y=1934422
+Sensor at x=685737, y=2465261: closest beacon is at x=1581951, y=2271709
+Sensor at x=1458348, y=2739442: closest beacon is at x=1581951, y=2271709
+Sensor at x=3742876, y=2811554: closest beacon is at x=3133845, y=3162635
+Sensor at x=437819, y=638526: closest beacon is at x=-101830, y=2000000
+Sensor at x=2537979, y=1762726: closest beacon is at x=2882446, y=1934422
+Sensor at x=1368739, y=2222863: closest beacon is at x=1581951, y=2271709
+Sensor at x=2743572, y=3976937: closest beacon is at x=2229474, y=3709584
+Sensor at x=2180640, y=105414: closest beacon is at x=3011118, y=-101788
+Sensor at x=3845753, y=474814: closest beacon is at x=3011118, y=-101788
+Sensor at x=2493694, y=3828087: closest beacon is at x=2229474, y=3709584
+Sensor at x=2786014, y=3388077: closest beacon is at x=3133845, y=3162635
+Sensor at x=3593418, y=3761871: closest beacon is at x=3133845, y=3162635
+Sensor at x=856288, y=3880566: closest beacon is at x=2229474, y=3709584
+Sensor at x=1757086, y=2518373: closest beacon is at x=1581951, y=2271709
+Sensor at x=2853518, y=2939097: closest beacon is at x=3133845, y=3162635
+Sensor at x=1682023, y=1449902: closest beacon is at x=1581951, y=2271709
+Sensor at x=3360575, y=1739100: closest beacon is at x=2882446, y=1934422
+Sensor at x=2904259, y=1465606: closest beacon is at x=2882446, y=1934422
+Sensor at x=3078500, y=3564862: closest beacon is at x=3133845, y=3162635
+Sensor at x=2835288, y=1011055: closest beacon is at x=2882446, y=1934422
+Sensor at x=2998762, y=2414323: closest beacon is at x=2882446, y=1934422

day15/src/main.rs

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+use regex::Regex;
+use std::ops::Range;
+
+#[derive(Debug)]
+struct Sensor {
+    location: (isize, isize),
+    beacon: (isize, isize),
+    reach: isize,
+}
+
+fn main() {
+    let contents = std::fs::read_to_string("data.txt").expect("Failed to read file");
+    let sensors = contents.lines().map(parse).collect::<Vec<Sensor>>();
+
+    // Part 1
+    let row = 2000000;
+    let mut reached = 0;
+    let range = find_range(&sensors);
+    for col in range {
+        let p = (col, row);
+        // if this cell has a beacon or sensor, it can' be here
+        if sensors.iter().any(|s| s.beacon == p) {
+            continue;
+        }
+        // if any of the beacons can reach this cell, count it
+        if sensors.iter().any(|s| can_reach(s, p)) {
+            reached += 1;
+        }
+    }
+    println!("Reached {reached}");
+
+    // Part 2
+    let max = 4_000_000;
+    // Look in a diamond shape just outside of each sensor's reach
+    'outer: for s in &sensors {
+        let per = perimeter(&s)
+            .into_iter()
+            .filter(|c| c.0 <= max && c.0 >= 0 && c.1 <= max && c.1 >= 0)
+            .collect::<Vec<(isize, isize)>>();
+        for coord in per {
+            if sensors.iter().any(|s| can_reach(s, coord)) {
+                continue;
+            } else {
+                println!("Found it: {:?}", coord);
+                let freq = coord.0 * 4000000 + coord.1;
+                println!("Tuning Frequency: {:?}", freq);
+                break 'outer;
+            }
+        }
+    }
+}
+
+fn parse(str: &str) -> Sensor {
+    let re = Regex::new(r"Sensor at x=(.*), y=(.*): closest beacon is at x=(.*), y=(.*)").unwrap();
+    let c = re.captures(str).unwrap();
+    let p = (1..=4)
+        .map(|i| c.get(i).unwrap().as_str().parse().unwrap())
+        .collect::<Vec<isize>>();
+
+    let location = (p[0], p[1]);
+    let beacon = (p[2], p[3]);
+    let reach = distance(location, beacon);
+    Sensor {
+        location,
+        beacon,
+        reach,
+    }
+}
+
+fn distance(p1: (isize, isize), p2: (isize, isize)) -> isize {
+    let (x1, y1) = p1;
+    let (x2, y2) = p2;
+    (x1 - x2).abs() + (y1 - y2).abs()
+}
+
+fn can_reach(s: &Sensor, p: (isize, isize)) -> bool {
+    distance(s.location, p) <= s.reach
+}
+
+fn find_range(sensors: &Vec<Sensor>) -> Range<isize> {
+    let mut min = 0;
+    let mut max = 0;
+
+    for s in sensors {
+        let leftmost = s.location.0 - s.reach;
+        if leftmost < min {
+            min = leftmost;
+        }
+
+        let rightmost = s.location.1 + s.reach;
+        if rightmost > max {
+            max = rightmost;
+        }
+    }
+    min..max
+}
+
+fn perimeter(s: &Sensor) -> Vec<(isize, isize)> {
+    let mut coords = vec![];
+    let length = s.reach + 2;
+
+    // start on the left, then go clockwise around the sensor's range
+    let (mut col, mut row) = (s.location.0 - s.reach - 1, s.location.1);
+    for i in 0..=length {
+        coords.push((col + i, row - i));
+    }
+    // from the top, down and right
+    (col, row) = (s.location.0, s.location.1 - s.reach - 1);
+    for i in 0..=length {
+        coords.push((col + i, row + i));
+    }
+
+    // from the right, going down and left
+    (col, row) = (s.location.0 + s.reach + 1, s.location.1);
+    for i in 0..=length {
+        coords.push((col - i, row + i));
+    }
+
+    // from the bottom, going up and left
+    (col, row) = (s.location.0, s.location.1 + s.reach + 1);
+    for i in 0..=length {
+        coords.push((col - i, row - i));
+    }
+
+    coords
+}

day15/test.txt

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+Sensor at x=2, y=18: closest beacon is at x=-2, y=15
+Sensor at x=9, y=16: closest beacon is at x=10, y=16
+Sensor at x=13, y=2: closest beacon is at x=15, y=3
+Sensor at x=12, y=14: closest beacon is at x=10, y=16
+Sensor at x=10, y=20: closest beacon is at x=10, y=16
+Sensor at x=14, y=17: closest beacon is at x=10, y=16
+Sensor at x=8, y=7: closest beacon is at x=2, y=10
+Sensor at x=2, y=0: closest beacon is at x=2, y=10
+Sensor at x=0, y=11: closest beacon is at x=2, y=10
+Sensor at x=20, y=14: closest beacon is at x=25, y=17
+Sensor at x=17, y=20: closest beacon is at x=21, y=22
+Sensor at x=16, y=7: closest beacon is at x=15, y=3
+Sensor at x=14, y=3: closest beacon is at x=15, y=3
+Sensor at x=20, y=1: closest beacon is at x=15, y=3