From 0e5d98d1bc59801be4a653409b417f9ed62ae91e Mon Sep 17 00:00:00 2001
From: Johannes <freelon@gmx.net>
Date: Mon, 20 Oct 2025 23:49:10 +0200
Subject: [PATCH] day 18 rust part 2

---
 src/day18.rs | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 src/day18.rs

diff --git a/src/day18.rs b/src/day18.rs
new file mode 100644
index 0000000..462693d
--- /dev/null
+++ b/src/day18.rs
@@ -0,0 +1,120 @@
+use std::{
+    collections::{HashMap, HashSet, VecDeque},
+    fs::read_to_string,
+};
+
+use itertools::Itertools;
+
+pub fn day_main() {
+    let input = read_to_string("input/day18.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    solve1(input, 1024, 70)
+}
+
+fn solve1(input: &str, n: usize, coord_max: i32) -> usize {
+    let points = parse(input);
+    sp(&points[..n], coord_max).unwrap()
+}
+
+fn sp(points: &[(i32, i32)], coord_max: i32) -> Option<usize> {
+    let pointss: HashSet<&(i32, i32)> = HashSet::from_iter(points);
+    let mut visited = HashMap::new();
+    let mut queue = VecDeque::from_iter([(0, 0, 0)]);
+    while let Some((x, y, c)) = queue.pop_front() {
+        if x == coord_max && y == coord_max {
+            return Some(c);
+        }
+
+        if visited.contains_key(&(x, y)) {
+            continue;
+        }
+        visited.insert((x, y), c);
+
+        for (dx, dy) in [(0, 1), (1, 0), (0, -1), (-1, 0)] {
+            let (a, b) = (x + dx, y + dy);
+            if (0..=coord_max).contains(&a)
+                && (0..=coord_max).contains(&b)
+                && !pointss.contains(&(a, b))
+            {
+                queue.push_back((a, b, c + 1));
+            }
+        }
+    }
+    None
+}
+
+fn parse(input: &str) -> Vec<(i32, i32)> {
+    input
+        .trim()
+        .lines()
+        .map(|line| {
+            line.split(",")
+                .map(|v| v.parse().unwrap())
+                .collect_tuple()
+                .unwrap()
+        })
+        .collect_vec()
+}
+
+fn part2(input: &str) -> String {
+    solve2(input, 1024, 70)
+}
+
+fn solve2(input: &str, fixed: usize, max_coord: i32) -> String {
+    let points = parse(input);
+    for i in fixed..points.len() {
+        if let None = sp(&points[..=i], max_coord) {
+            return format!("{},{}", points[i].0, points[i].1);
+        }
+    }
+    unreachable!()
+}
+
+#[cfg(test)]
+mod test {
+    use crate::day18::{solve1, solve2};
+
+    const TEST_INPUT: &str = r"5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(solve1(TEST_INPUT, 12, 6), 22);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(solve2(TEST_INPUT, 12, 6), "6,1");
+    }
+}