From 4a2e0fef5534a26f22d852a3b60aeccee46a2956 Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Sat, 9 Dec 2023 13:20:31 +0100
Subject: [PATCH] =?UTF-8?q?day(09):=20do=20=E2=80=B9find=5Fnext=E2=80=BA?=
 =?UTF-8?q?=20in-situ?=
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Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 src/bin/day09.rs | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/bin/day09.rs b/src/bin/day09.rs
index 81bb313..dedf28e 100644
--- a/src/bin/day09.rs
+++ b/src/bin/day09.rs
@@ -8,18 +8,20 @@ struct Day09 {
 }
 
 impl Day09 {
-    fn find_next(xs: &[i32]) -> i32 {
+    fn find_next(mut xs: Vec<i32>) -> i32 {
+        let last = *xs.last().unwrap();
+
         let mut ds = vec![];
+        while xs.iter().any(|&x| x != 0) {
+            for i in 0..xs.len() - 1 {
+                xs[i] = xs[i + 1] - xs[i];
+            }
+            xs.pop();
 
-        let mut last_row = xs.to_owned();
-        while last_row.iter().any(|&x| x != 0) {
-            let next_row = last_row.windows(2).map(|s| s[1] - s[0]).collect_vec();
-
-            ds.push(*next_row.last().unwrap());
-            last_row = next_row;
+            ds.push(*xs.last().unwrap());
         }
 
-        xs.last().unwrap() + ds.iter().rev().sum::<i32>()
+        last + ds.iter().rev().sum::<i32>()
     }
 }
 
@@ -34,7 +36,7 @@ impl Solution<Output1, Output2> for Day09 {
     }
 
     fn part_1(&mut self) -> Output1 {
-        self.values.iter().map(|xs| Self::find_next(xs)).sum()
+        self.values.iter().cloned().map(Self::find_next).sum()
     }
 
     fn part_2(&mut self) -> Output2 {
@@ -46,7 +48,7 @@ impl Solution<Output1, Output2> for Day09 {
 
                 ys
             })
-            .map(|xs| Self::find_next(&xs))
+            .map(Self::find_next)
             .sum()
     }
 }