AoC_2025/Day07.cs

@@ -29,14 +29,14 @@ public class Day07 : IPuzzleSolver<long>
     {
         var grid = ParsePuzzleInput(pathToPuzzleInput);
         var start = GetStart(grid);
-        var nodesWithCount = GetTimelinesCountRecursive(grid, start, []);
-        return nodesWithCount;
+        var nodesWithCount = GetNodesTraversedWitTimelineCount(grid, start, [], []);
+        return nodesWithCount[start];
     }
     
     public long SolvePart2Again(string pathToPuzzleInput)
     {
         var grid = ParsePuzzleInput(pathToPuzzleInput);
-        var nodesWithCount = GetTimelinesCount(grid);
+        var nodesWithCount = GetNodesTraversedWitTimelineCount(grid);
         return nodesWithCount.Sum();
     }
 
@@ -76,29 +76,40 @@ public class Day07 : IPuzzleSolver<long>
         }
     }
 
-    // Dictionary only for memoization
-    private long GetTimelinesCountRecursive(string[] grid, Coordinate current, Dictionary<Coordinate, long> memory)
+    private Dictionary<Coordinate, long> GetNodesTraversedWitTimelineCount(string[] grid, Coordinate current, HashSet<Coordinate> path, Dictionary<Coordinate, long> nodeCountVisited)
     {
-        if (current.x >= grid.Length)
+        if (current.x >= grid.Length || nodeCountVisited.ContainsKey(current))
         {
-            return 1;
+            nodeCountVisited = UpdateNodeVisitedCounts(current, path, nodeCountVisited);
+            return nodeCountVisited;
         }
-        if(memory.TryGetValue(current, out var count)) return count;
+
+        nodeCountVisited[current] = 0;
+        path.Add(current);
 
         if (grid[current.x][current.y] == '^')
         {
-            var resLeft = GetTimelinesCountRecursive(grid, (current.x, current.y - 1), memory);
-            var resRight = GetTimelinesCountRecursive(grid, (current.x, current.y + 1), memory);
-            memory[current] = resLeft + resRight;
-            return resLeft + resRight;
+            var resLeft = GetNodesTraversedWitTimelineCount(grid, (current.x, current.y - 1), [..path], nodeCountVisited);
+            var resRight = GetNodesTraversedWitTimelineCount(grid, (current.x, current.y + 1), [..path], resLeft);
+            return resRight;
         }
 
-        var res = GetTimelinesCountRecursive(grid, (current.x + 1, current.y), memory);
-        memory[current] = res;
+        var res = GetNodesTraversedWitTimelineCount(grid, (current.x + 1, current.y), [..path], nodeCountVisited);
         return res;
     }
 
-    private long[] GetTimelinesCount(string[] grid)
+    private static Dictionary<Coordinate, long> UpdateNodeVisitedCounts(Coordinate current, HashSet<Coordinate> path, Dictionary<Coordinate, long> nodeCountVisited)
+    {
+        var addAmount = nodeCountVisited.GetValueOrDefault(current, 1);
+        foreach (var node in path)
+        {
+            nodeCountVisited[node] += addAmount;
+        }
+
+        return nodeCountVisited;
+    }
+
+    private long[] GetNodesTraversedWitTimelineCount(string[] grid)
     {
         var numbersGrid = grid
             .Select(line => line.Select(c => 0L).ToArray())