From b84bb5aa6b3139a2a097c7ece914bf1866d6a162 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Tue, 19 Nov 2024 22:06:52 +0100
Subject: aoc 2015, day 20

---
 2015/src/day20.cpp | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 2015/src/day20.cpp

diff --git a/2015/src/day20.cpp b/2015/src/day20.cpp
new file mode 100644
index 0000000..85e3539
--- /dev/null
+++ b/2015/src/day20.cpp
@@ -0,0 +1,52 @@
+#include <iostream>
+#include <unordered_map>
+using namespace std;
+
+void
+part1(int limit)
+{
+	unordered_map<int, int> house;
+
+	for ( int i = 1; i < limit / 10; ++i ) {
+		for ( int j = i; j < limit / 10; j += i ) {
+			house[j] += i * 10;
+		}
+	}
+
+	for ( int i = 0;; ++i ) {
+		if ( house[i] >= limit ) {
+			cout << i << endl;
+			return;
+		}
+	}
+}
+
+void
+part2(int limit)
+{
+	unordered_map<int, int> house;
+
+	for ( int i = 1; i < limit / 10; ++i ) {
+		int visits = 0;
+		for ( int j = i; j < limit / 10; j += i ) {
+			if ( visits++ < 50 ) {
+				house[j] += i * 11;
+			}
+		}
+	}
+
+	for ( int i = 0;; ++i ) {
+		if ( house[i] >= limit ) {
+			cout << i << endl;
+			return;
+		}
+	}
+}
+
+int
+main()
+{
+	static const auto limit = 29000000;
+	part1(limit);
+	part2(limit);
+}
-- 
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