1 files changed, 52 insertions, 0 deletions

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);
+}