From b3bf7b2a97b5c8c8294568e4e8f9ffd01b374b3c Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Sat, 9 Dec 2023 14:11:16 +0100
Subject: [PATCH] optimize

---
 2023/day09/src/less_alloc.rs | 48 ++++++++++++++++++++++++++++++++++++
 2023/day09/src/lib.rs        |  4 +++
 2 files changed, 52 insertions(+)
 create mode 100644 2023/day09/src/less_alloc.rs

diff --git a/2023/day09/src/less_alloc.rs b/2023/day09/src/less_alloc.rs
new file mode 100644
index 0000000..68a5714
--- /dev/null
+++ b/2023/day09/src/less_alloc.rs
@@ -0,0 +1,48 @@
+use std::ops::Add;
+
+fn parse(input: &str) -> impl Iterator<Item = impl Iterator<Item = i64> + '_> + '_ {
+    input
+        .lines()
+        .map(|line| line.split_ascii_whitespace().map(|s| s.parse().unwrap()))
+}
+fn execute(
+    input: impl Iterator<Item = impl Iterator<Item = i64>>,
+    last_or_first: impl Fn(&[i64]) -> i64,
+    fold: impl Fn(i64, i64) -> i64 + Copy,
+) -> i64 {
+    let mut values = Vec::with_capacity(128);
+    let mut derive = Vec::with_capacity(128);
+
+    let mut last_values = Vec::with_capacity(16);
+
+    input
+        .map(|values_iter| {
+            values.clear();
+
+            values.extend(values_iter);
+            derive.clone_from(&values);
+
+            last_values.clear();
+            last_values.push(last_or_first(&values));
+
+            while !derive.iter().all(|&n| n == 0) {
+                values.clear();
+                values.extend(derive.windows(2).map(|s| s[1] - s[0]));
+
+                last_values.push(last_or_first(&values));
+
+                std::mem::swap(&mut values, &mut derive);
+            }
+
+            last_values.iter().copied().rev().fold(0, fold)
+        })
+        .sum::<i64>()
+}
+
+pub fn part1(input: &str) -> u64 {
+    execute(parse(input), |s| *s.last().unwrap(), Add::add) as u64
+}
+
+pub fn part2(input: &str) -> u64 {
+    execute(parse(input), |s| *s.first().unwrap(), |a, b| b - a) as u64
+}
diff --git a/2023/day09/src/lib.rs b/2023/day09/src/lib.rs
index 7314d6b..47905f3 100644
--- a/2023/day09/src/lib.rs
+++ b/2023/day09/src/lib.rs
@@ -1,3 +1,5 @@
+mod less_alloc;
+
 use std::ops::Add;
 
 use helper::{Day, Variants};
@@ -12,9 +14,11 @@ helper::define_variants! {
     day => crate::Day09;
     part1 {
         basic => crate::part1;
+        less_alloc => crate::less_alloc::part1;
     }
     part2 {
         basic => crate::part2;
+        less_alloc => crate::less_alloc::part2;
     }
 }