aoc 2024, day 18, part 2

1 files changed, 38 insertions, 5 deletions

diff --git a/2024/src/day18.cpp b/2024/src/day18.cpp
index fedd836..b77650a 100644
--- a/2024/src/day18.cpp
+++ b/2024/src/day18.cpp
@@ -26,8 +26,8 @@ read_file(string_view filename)
         return data;
 }
 
-void
-part1(const vector<pos_type>& data, long size)
+optional<long>
+bfs(const vector<pos_type>& data, long size)
 {
         set<pos_type> stones{ data.begin(), data.end() };
 
@@ -44,8 +44,7 @@ part1(const vector<pos_type>& data, long size)
                 const auto [x, y] = pos;
 
                 if ( x == size && y == size ) {
-                        cout << distance << endl;
-                        return;
+                        return distance;
                 }
 
                 if ( x < 0 || y < 0 || x > size || y > size ) {
@@ -65,11 +64,45 @@ part1(const vector<pos_type>& data, long size)
                         queue.push({ { nx, ny }, distance + 1 });
                 }
         }
+        return nullopt;
+}
+
+void
+part1(const vector<pos_type>& data, long size)
+{
+        if ( auto result = bfs(data, size) ) {
+                cout << *result << endl;
+        }
+}
+
+void
+part2(const vector<pos_type>& data, long size)
+{
+        for ( size_t i = 0; i != data.size(); ++i ) {
+                const vector<pos_type> foo{ data.begin(), data.begin() + ptrdiff_t(i) };
+
+                if ( !bfs(foo, size) ) {
+                        const auto& [x, y] = foo.back();
+                        cout << x << "," << y << endl;
+                        return;
+                }
+        }
 }
 
 int
 main()
 {
+#if 0
+        const auto data = read_file("data/day18-sample1.txt");
+        const long size = 6;
+
+        part1({ data.begin(), data.begin() + 12 }, size);
+        part2(data, size);
+#else
         const auto data = read_file("data/day18.txt");
-        part1({ data.begin(), data.begin() + 1024 }, 70);
+        const long size = 70;
+
+        part1({ data.begin(), data.begin() + 1024 }, size);
+        part2(data, size);
+#endif
 }