From 827acfa3ef141939665fafab8019153519ddd9fb Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sat, 9 Dec 2023 11:36:07 +0100
Subject: Clean up

---
 src/day09.cpp | 49 +++++++++++++++++--------------------------------
 1 file changed, 17 insertions(+), 32 deletions(-)

(limited to 'src')

diff --git a/src/day09.cpp b/src/day09.cpp
index 1afcfe2..1e9bde5 100644
--- a/src/day09.cpp
+++ b/src/day09.cpp
@@ -27,25 +27,21 @@ read_ints(const string& line)
 }
 
 template<typename T>
-void
-solve_rec_part1(vector<T>& values)
+T
+solve_rec_part1(const vector<T>& values)
 {
 	vector<T> differences;
 
 	for ( size_t idx = 1; idx < values.size(); ++idx ) {
-		auto difference = values[idx] - values[idx - 1];
-		differences.emplace_back(difference);
+		differences.emplace_back(values[idx] - values[idx - 1]);
 	}
-	auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
-	if ( !all_zeros) {
-		solve_rec_part1(differences);
+	auto all_zeros = all_of(differences.begin(), differences.end(), [](T diff) { return diff == 0; });
+	if ( !all_zeros ) {
+		return solve_rec_part1(differences) + values.back();
 	}
 	else {
-		differences.emplace_back(0);
+		return values.back();
 	}
-	auto last_value = values.back();
-	auto last_difference = differences.back();
-	values.emplace_back(last_value + last_difference);
 }
 
 void
@@ -55,46 +51,35 @@ part1()
 
 	long sum = 0;
 	for ( const auto& line: lines ) {
-		auto values = read_ints(line);
-		solve_rec_part1(values);
-		sum += values.back();
+		sum += solve_rec_part1(read_ints(line));
 	}
 	cout << sum << endl;
 }
 
 template<typename T>
-void
-solve_rec_part2(vector<T>& values)
+T
+solve_rec_part2(const vector<T>& values)
 {
 	vector<T> differences;
 
 	for ( size_t idx = 1; idx < values.size(); ++idx ) {
-		auto difference = values[idx] - values[idx - 1];
-		differences.emplace_back(difference);
+		differences.emplace_back(values[idx] - values[idx - 1]);
 	}
-	auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
-	if ( !all_zeros) {
-		solve_rec_part2(differences);
+	auto all_zeros = all_of(differences.begin(), differences.end(), [](T diff) { return diff == 0; });
+	if ( !all_zeros ) {
+		return values.front() - solve_rec_part2(differences);
 	}
 	else {
-		differences.insert(differences.begin(), 0);
+		return values.front();
 	}
-
-	auto first_value = values.front();
-	auto first_difference = differences.front();
-	values.insert(values.begin(), first_value - first_difference);
 }
 
 void
 part2()
 {
-	auto lines = read_file("data/day09.txt");
-
 	long sum = 0;
-	for ( const auto& line: lines ) {
-		auto values = read_ints(line);
-		solve_rec_part2(values);
-		sum += values.front();
+	for ( const auto& line: read_file("data/day09.txt") ) {
+		sum += solve_rec_part2(read_ints(line));
 	}
 	cout << sum << endl;
 }
-- 
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