From 3f1e9844dbe58428e3b9528e9418c363266ceae4 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 19 Nov 2025 23:18:20 +0100
Subject: aoc 2018, days 13 & 14

---
 2018/src/day14.cpp | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 2018/src/day14.cpp

(limited to '2018/src/day14.cpp')

diff --git a/2018/src/day14.cpp b/2018/src/day14.cpp
new file mode 100644
index 0000000..95d0717
--- /dev/null
+++ b/2018/src/day14.cpp
@@ -0,0 +1,88 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+void
+part1(const size_t n)
+{
+	vector<size_t> v{ 3, 7 };
+	size_t         first  = 0;
+	size_t         second = 1;
+
+	while ( v.size() < n + 10 ) {
+		auto value = v[first] + v[second];
+		if ( value >= 10 ) {
+			v.emplace_back(1);
+			value -= 10;
+		}
+		v.emplace_back(value);
+
+		first  = (first + v[first] + 1) % v.size();
+		second = (second + v[second] + 1) % v.size();
+	}
+
+	cout << "Part 1: ";
+	for ( size_t i = n; i != n + 10; ++i ) {
+		cout << v[i];
+	}
+	cout << '\n';
+}
+
+void
+part2(const size_t n)
+{
+	vector<size_t> v{ 3, 7 };
+	size_t         first  = 0;
+	size_t         second = 1;
+
+	const size_t len = to_string(n).length();
+
+	auto check = [&] {
+		if ( v.size() < len ) {
+			return false;
+		}
+
+		size_t value = 0;
+		for ( size_t i = len; i > 0; --i ) {
+			value *= 10;
+			value += v[v.size() - i];
+		}
+
+		return value == n;
+	};
+
+	for ( ;; ) {
+		auto value = v[first] + v[second];
+		if ( value >= 10 ) {
+			v.emplace_back(1);
+			if ( check() ) {
+				break;
+			}
+
+			value -= 10;
+		}
+
+		v.emplace_back(value);
+		if ( check() ) {
+			break;
+		}
+
+		first  = (first + v[first] + 1) % v.size();
+		second = (second + v[second] + 1) % v.size();
+	}
+
+	cout << "Part 2: " << v.size() - len << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	const size_t input = 607331;
+	part1(input);
+	part2(input);
+}
-- 
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