aoc 2024, day 10, part 2

1 files changed, 51 insertions, 3 deletions

diff --git a/2024/src/day10.cpp b/2024/src/day10.cpp
index 43dbd6e..58b797f 100644
--- a/2024/src/day10.cpp
+++ b/2024/src/day10.cpp
@@ -33,10 +33,10 @@ neighbors(pos_type pos)
         return { { x - 1, y }, { x, y - 1 }, { x + 1, y }, { x, y + 1 } };
 }
 
-long
+size_t
 bfs(const map<pos_type, int>& data, pos_type start_pos)
 {
-        long peaks = 0;
+        size_t peaks = 0;
 
         set<pos_type>   seen;
         queue<pos_type> queue;
@@ -77,16 +77,64 @@ part1(const map<pos_type, int>& data)
                 }
         }
 
-        long sum = 0;
+        size_t sum = 0;
         for ( const auto& start: starts ) {
                 sum += bfs(data, start);
         }
         cout << sum << endl;
 }
 
+size_t
+bfs2(const map<pos_type, int>& data, pos_type start_pos)
+{
+        size_t paths = 0;
+
+        queue<pos_type> queue;
+
+        queue.push(start_pos);
+
+        while ( !queue.empty() ) {
+                auto pos = queue.front();
+                queue.pop();
+
+                if ( data.at(pos) == 9 ) {
+                        ++paths;
+                        continue;
+                }
+
+                for ( const auto& neighbor: neighbors(pos) ) {
+                        if ( !data.contains(neighbor) ||
+                             data.at(neighbor) != data.at(pos) + 1 ) {
+                                continue;
+                        }
+
+                        queue.emplace(neighbor);
+                }
+        }
+        return paths;
+}
+
+void
+part2(const map<pos_type, int>& data)
+{
+        vector<pos_type> starts;
+        for ( const auto& [pos, value]: data ) {
+                if ( value == 0 ) {
+                        starts.push_back(pos);
+                }
+        }
+
+        size_t sum = 0;
+        for ( const auto& start: starts ) {
+                sum += bfs2(data, start);
+        }
+        cout << sum << endl;
+}
+
 int
 main()
 {
         auto data = read_file("data/day10.txt");
         part1(data);
+        part2(data);
 }