From 21880ee880d321e760b6b560db0696c8af4c98d9 Mon Sep 17 00:00:00 2001
From: alyx <alyx@aleteoryx.me>
Date: Sun, 3 Dec 2023 02:43:18 -0500
Subject: 2023.3

---
 2023/rs/code/three/src/main.rs | 96 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 2023/rs/code/three/src/main.rs

(limited to '2023/rs/code/three/src/main.rs')

diff --git a/2023/rs/code/three/src/main.rs b/2023/rs/code/three/src/main.rs
new file mode 100644
index 0000000..c72abe9
--- /dev/null
+++ b/2023/rs/code/three/src/main.rs
@@ -0,0 +1,96 @@
+#![feature(iter_map_windows)]
+
+use std::collections::BTreeSet;
+
+static INPUT: &[u8] = include_bytes!("input.txt");
+
+#[derive(Copy, Clone, Debug)]
+enum LineMaskEntry {
+  Empty,
+  Gear,
+  Number{tag: u32, num: u32}
+}
+
+fn main() {
+  let valueified = INPUT.split(|b| *b == b'\n').filter(|s| !s.is_empty());
+
+  let mut num = 0;
+
+  let (parts_number_sum, gears_mask) = [valueified.clone().next().unwrap()].into_iter().chain(valueified.clone()).chain([valueified.clone().last().unwrap()])
+    .map_windows::<_, _, 3>(|[prev, curr, next]| {
+      let mut numlen = 0;
+      let mut numval = 0;
+
+      let mut acc = 0;
+      let mut linemask = vec![LineMaskEntry::Empty; curr.len()];
+
+      for i in 0..curr.len() {
+        if curr[i] == b'*' { linemask[i] = LineMaskEntry::Gear; }
+
+        if !curr[i].is_ascii_digit() && numlen != 0 {
+          let start = if i - numlen == 0 { i - numlen } else { i - numlen - 1 };
+          let end = i;
+          let window = || start..=end;
+          if prev[window()].into_iter().chain(&curr[window()]).chain(&next[window()]).any(|b| !b.is_ascii_digit() && *b != b'.') {
+            acc += numval;
+
+            linemask[i - numlen .. i].fill(LineMaskEntry::Number{ tag: num, num: numval });
+            num += 1;
+          }
+
+          numlen = 0;
+          numval = 0;
+        }
+        else if curr[i].is_ascii_digit() {
+          numlen += 1;
+          numval *= 10;
+          numval += (curr[i] - b'0') as u32;
+        }
+      }
+
+      if numlen != 0 {
+        let window = || curr.len() - numlen - 1..curr.len();
+        if prev[window()].into_iter().chain(&curr[window()]).chain(&next[window()]).any(|b| !b.is_ascii_digit() && *b != b'.') {
+          acc += numval;
+
+          linemask[curr.len() - numlen .. curr.len()].fill(LineMaskEntry::Number{ tag: num, num: numval });
+          num += 1;
+        }
+      }
+      (acc, linemask)
+    }).fold((0, Vec::new()), |(n, mut v), (a, l)| (n + a, {v.push(l); v}));
+  println!("Sum of valid part numbers: {parts_number_sum}");
+
+
+  let first = vec![LineMaskEntry::Empty; gears_mask[0].len()];
+  let last = first.clone();
+  let gear_ratio_sum = [first].into_iter().chain(gears_mask).chain([last])
+    .map_windows::<_, _, 3>(|[prev, curr, next]| {
+      let mut acc = 0;
+
+      for i in 0..curr.len() {
+        match curr[i] {
+          LineMaskEntry::Gear => {
+            let mut set = BTreeSet::new();
+            for row in [prev, curr, next] {
+              for n in [i - 1, i, i + 1] {
+                if n == 0 || n == row.len() { continue; }
+                if let LineMaskEntry::Number{tag, num} = row[n] {
+                  set.insert((tag, num));
+                }
+              }
+            }
+            if set.len() == 2 {
+              let mut iter = set.into_iter();
+              let x = iter.next().unwrap().1;
+              let y = iter.next().unwrap().1;
+              acc += x * y
+            }
+          },
+          _ => ()
+        }
+      }
+      acc
+    }).sum::<u32>();
+  println!("Gear ratio sum: {gear_ratio_sum}");
+}
-- 
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