From 1092f82f162bbc6f55c47825512e0a45d67357ba Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Mon, 1 Dec 2025 21:57:43 +0100
Subject: aoc 2025, day 1, cleanup & optimized version for P2

---
 2025/src/day01.cpp | 47 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/2025/src/day01.cpp b/2025/src/day01.cpp
index aa1ea42..2650b3c 100644
--- a/2025/src/day01.cpp
+++ b/2025/src/day01.cpp
@@ -28,8 +28,7 @@ part1(const vector<string>& lines)
 	auto pos   = 50;
 
 	for ( const auto& line: lines ) {
-		auto value = stoi(line.substr(1));
-		value %= 100;
+		const auto value = stoi(line.substr(1)) % 100;
 		pos += (line[0] == 'L') ? (100 - value) : value;
 		if ( pos % 100 == 0 ) {
 			++zeros;
@@ -45,9 +44,9 @@ part2(const vector<string>& lines)
 	auto pos   = 50;
 
 	for ( const auto& line: lines ) {
-		auto value = stoi(line.substr(1));
-		while ( value-- > 0 ) {
-			pos += (line[0] == 'L') ? 99 : 1;
+		const auto delta = (line[0] == 'L') ? 99 : 1;
+		for ( auto value = stoi(line.substr(1)); value > 0; --value ) {
+			pos += delta;
 			if ( pos % 100 == 0 ) {
 				++zeros;
 			}
@@ -56,6 +55,43 @@ part2(const vector<string>& lines)
 	cout << "Part 2: " << zeros << '\n';
 }
 
+void
+part2_opti(const vector<string>& lines)
+{
+	auto zeros = 0;
+	auto pos   = 50;
+
+	auto is_zero = [&pos] {
+		return pos % 100 == 0;
+	};
+
+	for ( const auto& line: lines ) {
+		const auto delta = (line[0] == 'L') ? 99 : 1;
+		auto       value = stoi(line.substr(1));
+
+		if ( !is_zero() ) {
+			for ( ; value > 0 && !is_zero(); --value ) {
+				pos += delta;
+			}
+
+			if ( is_zero() ) {
+				++zeros;
+			}
+		}
+
+		zeros += value / 100;
+		value %= 100;
+
+		for ( ; value > 0; --value ) {
+			pos += delta;
+			if ( is_zero() ) {
+				++zeros;
+			}
+		}
+	}
+	cout << "Part2 (Opti): " << zeros << '\n';
+}
+
 } // namespace
 
 int
@@ -64,4 +100,5 @@ main()
 	auto data = read_file("data/day01.txt");
 	part1(data);
 	part2(data);
+	part2_opti(data);
 }
-- 
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