From 55688a124d845fed3f48f6325cceb6ba99673a39 Mon Sep 17 00:00:00 2001
From: YK <yk@qcl.one>
Date: Fri, 6 Dec 2024 12:53:08 +0300
Subject: [PATCH] solution: day 6

---
 src/days.rs    |   2 +-
 src/days/d6.rs | 131 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 132 insertions(+), 1 deletion(-)
 create mode 100644 src/days/d6.rs

diff --git a/src/days.rs b/src/days.rs
index 4436c45..a44c1c7 100644
--- a/src/days.rs
+++ b/src/days.rs
@@ -3,7 +3,7 @@ pub mod d2;
 pub mod d3;
 pub mod d4;
 pub mod d5;
-// pub mod d6;
+pub mod d6;
 // pub mod d7;
 // pub mod d8;
 // pub mod d9;
diff --git a/src/days/d6.rs b/src/days/d6.rs
new file mode 100644
index 0000000..1acaf1a
--- /dev/null
+++ b/src/days/d6.rs
@@ -0,0 +1,131 @@
+#![allow(non_upper_case_globals)]
+use crate::prelude::*;
+
+pub type I = Vec<Vec<char>>;
+pub type O = usize;
+
+fn _parse (data: &str) -> I {
+    data.lines().map(|line| line.chars().collect()).collect()
+}
+
+fn _traverse (data: &I) -> S<(usize, usize)> {
+    let (mut sy, mut sx) = data.iter().enumerate().find_map(|(y, row)| row.iter().position(|e| *e == '^').map(|x| (y, x))).unwrap();
+
+    let rows = data.len();
+    let cols = data[0].len();
+
+    let mut s: S<(usize, usize)> = S::new();
+    const dirs: [(isize, isize); 4] = [(-1, 0), (0, 1), (1, 0), (0, -1)];
+    let mut dir = 0;
+
+    loop {
+
+        let (dy, dx) = dirs[dir];
+        let ny = sy.checked_add_signed(dy);
+        let nx = sx.checked_add_signed(dx);
+
+        match (ny, nx) {
+            (Some(ny), Some(nx)) if ny < rows && nx < cols => {
+                if data[ny][nx] == '#' {
+                    dir = (dir + 1) % 4;
+                } else {
+                    s.insert((ny, nx));
+                    sy = ny;
+                    sx = nx;
+                }
+            },
+            _ => break,
+        }
+
+    }
+
+    s
+}
+
+fn _silver (data: I) -> O {
+    let ans = _traverse(&data);
+    ans.len()
+}
+
+fn _gold (mut data: I) -> O {
+    let path = _traverse(&data);
+    let (sy, sx) = data.iter().enumerate().find_map(|(y, row)| row.iter().position(|e| *e == '^').map(|x| (y, x))).unwrap();
+    data[sy][sx] = '.';
+
+    let rows = data.len();
+    let cols = data[0].len();
+
+    const dirs: [(isize, isize); 4] = [(-1, 0), (0, 1), (1, 0), (0, -1)];
+
+    let mut loops = 0;
+
+    'outer : for (cy, cx) in path {
+        if cy == sy && cx == sx { continue; }
+        if data[cy][cx] == '.' {
+            data[cy][cx] = '#';
+
+            let mut y = sy;
+            let mut x = sx;
+
+            let mut s: S<((usize, usize), usize)> = S::new();
+            let mut dir = 0;
+
+            'inner : loop {
+                let (dy, dx) = dirs[dir];
+
+                if s.contains(&((y, x), dir)) {
+                    loops += 1;
+                    data[cy][cx] = '.';
+                    continue 'outer;
+                }
+                s.insert(((y, x), dir));
+
+                let ny = y.checked_add_signed(dy);
+                let nx = x.checked_add_signed(dx);
+
+                match (ny, nx) {
+                    (Some(ny), Some(nx)) if ny < rows && nx < cols => {
+                        if data[ny][nx] == '#' {
+                            dir = (dir + 1) % 4;
+                        } else {
+                            y = ny;
+                            x = nx;
+                        }
+                    },
+                    _ => break 'inner,
+                }
+
+            }
+
+            data[cy][cx] = '.';
+        }
+    }
+
+    loops
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        let data = inc!(6);
+        _parse(data)
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(data);
+
+        assert_eq!(ans, 4967)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(data);
+
+        assert_eq!(ans, 1789)
+    }
+}