From 75419df5eb7ac81cbd8ac631ca71bbbdae18a10a Mon Sep 17 00:00:00 2001
From: mhsn <mail@mhsn.net>
Date: Tue, 29 Apr 2025 19:27:22 +0100
Subject: 2024-02 rust p2

---
 2024/02/rust/src/main.rs | 37 ++++++++++++-------------------------
 1 file changed, 12 insertions(+), 25 deletions(-)

diff --git a/2024/02/rust/src/main.rs b/2024/02/rust/src/main.rs
index 620fe8b..2007837 100644
--- a/2024/02/rust/src/main.rs
+++ b/2024/02/rust/src/main.rs
@@ -1,3 +1,5 @@
+#![feature(iter_map_windows)]
+
 use std::io;
 
 fn main() {
@@ -12,35 +14,20 @@ fn main() {
         .collect::<Result<Vec<_>, _>>()
         .unwrap();
 
-    let silver: usize = input.iter().map(self::safe).flatten().count();
-    let gold: u64 = 0;
+    let silver: usize = input.iter().filter(|&xs| all_safe(xs)).count();
+    let gold: usize = input.iter().filter(|&xs| drop_safe(xs)).count();
     println!("silver: {silver}");
     println!("gold: {gold}");
 }
 
-#[derive(Debug, PartialEq)]
-enum Dir {
-    Asc,
-    Desc,
+fn all_safe(xs: &Vec<i64>) -> bool {
+    let mut diffs = xs.iter().map_windows(|&[x, y]| y - x).peekable();
+    let dir = diffs.peek().unwrap_or(&1).signum();
+    diffs.all(|d| (1..=3).contains(&d.abs()) && d.signum() == dir)
 }
 
-fn safe(xs: &Vec<i64>) -> Option<Dir> {
-    let mut dirs = xs
-        .iter()
-        .zip(xs.iter().skip(1))
-        .map(|(x, y)| y - x)
-        .map(|d| match d {
-            -3..=-1 => Some(Dir::Desc),
-            1..=3 => Some(Dir::Asc),
-            _ => None,
-        })
-        .collect::<Option<Vec<Dir>>>()?
-        .into_iter();
-
-    let head = dirs.next().unwrap_or(Dir::Asc);
-    if dirs.all(|d| d == head) {
-        Some(head)
-    } else {
-        None
-    }
+fn drop_safe(xs: &Vec<i64>) -> bool {
+    (0..xs.len())
+        .map(|idx| xs.split_at(idx))
+        .any(|(left, right)| all_safe(&[left, &right[1..]].concat()))
 }
-- 
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