aoc 2018, days 13 & 14aoc-2018

1 files changed, 88 insertions, 0 deletions

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);
+}