From 9a1f073f8e33e8b0d6c97332f51161683cfc6e58 Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Mon, 9 Dec 2024 14:06:37 +0100
Subject: Day 9 with views::reverse

---
 2024/09/day09a.cpp |  7 ++++---
 2024/09/day09b.cpp | 17 +++++++++--------
 2024/learned.txt   |  1 +
 2024/template.cpp  |  1 +
 4 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/2024/09/day09a.cpp b/2024/09/day09a.cpp
index c52c8f0..80732d7 100644
--- a/2024/09/day09a.cpp
+++ b/2024/09/day09a.cpp
@@ -1,6 +1,7 @@
 #include <algorithm>
 #include <iostream>
 #include <map>
+#include <ranges>
 #include <set>
 #include <sstream>
 #include <string>
@@ -16,11 +17,11 @@ int main() {
 			a.push_back(id % 2 == 0 ? id/2 : -1); // -1 = space
 
 	int j = 0;
-	for (int i = a.size()-1; i >= 0; i--) {
+	for (auto& x : a | views::reverse) {
 		while (a[j] >= 0) j++;
 		if (a[j] == -2) break;
-		a[j] = a[i];
-		a[i] = -2; // -2 = freed up
+		a[j] = x;
+		x = -2; // -2 = freed up
 	}
 
 	long long checksum = 0;
diff --git a/2024/09/day09b.cpp b/2024/09/day09b.cpp
index 3b1ac21..c304ed4 100644
--- a/2024/09/day09b.cpp
+++ b/2024/09/day09b.cpp
@@ -1,6 +1,7 @@
 #include <algorithm>
 #include <iostream>
 #include <map>
+#include <ranges>
 #include <set>
 #include <sstream>
 #include <string>
@@ -21,16 +22,16 @@ int main() {
 			a.push_back(id % 2 == 0 ? id/2 : -1); // -1 = space
 	}
 
-	for (int i = file.size()-1; i >= 0; i--) {
+	for (auto& p : file | views::reverse) {
 		for (auto& f : freesp) {
-			if (f.first >= file[i].first) break;
-			if (f.second >= file[i].second) {
-				for (int k = 0; k < file[i].second; k++) {
-					a[f.first+k] = a[file[i].first+k];
-					a[file[i].first+k] = -2;
+			if (f.first >= p.first) break;
+			if (f.second >= p.second) {
+				for (int k = 0; k < p.second; k++) {
+					a[f.first+k] = a[p.first+k];
+					a[p.first+k] = -2;
 				}
-				f.first += file[i].second;
-				f.second -= file[i].second;
+				f.first += p.second;
+				f.second -= p.second;
 				break;
 			}
 		}
diff --git a/2024/learned.txt b/2024/learned.txt
index 86d32ff..56fa515 100644
--- a/2024/learned.txt
+++ b/2024/learned.txt
@@ -7,3 +7,4 @@ List of things I learned (or refreshed) with this year's AoC.
   to assign two variables at once with a pair of references pair<int&, int&>
 * Day 5: std::find and std::replace
 * Day 8: set::insert_range(), but it is from C++23 only
+* Day 9: std::views
diff --git a/2024/template.cpp b/2024/template.cpp
index b2fd4ec..2475ae7 100644
--- a/2024/template.cpp
+++ b/2024/template.cpp
@@ -1,6 +1,7 @@
 #include <algorithm>
 #include <iostream>
 #include <map>
+#include <ranges>
 #include <set>
 #include <sstream>
 #include <string>
-- 
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