2024 - Day 10 - cleaned up a bit - no need to !! the gets from the ma…

…p - just appriciate them being null (reduces the number of filterings)

src/main/kotlin/no/rodland/advent_2024/Day10.kt

@@ -18,26 +18,25 @@ class Day10(val input: List<String>) : Day<Int, Int, Map<Pos, Int>> {
         return heads.sumOf { it.rating(emptyList(), mutableSetOf()) }
     }
 
-    private fun Pos.rating(path: List<Pos>, visited: MutableSet<List<Pos>>): Int {
-        val newPath = path + this
-        visited.add(newPath)
-        val c = grid[this]!!
-        return if (c == 9) 1
-        else neighbourCellsUDLR().filterNot { (newPath + it) in visited }
-            .filter { it in grid }
-            .filter { grid[it]!! == c + 1 }
-            .sumOf { it.rating(newPath, visited) }
+    private fun Pos.score(visited: MutableSet<Pos>): Int {
+        return grid[this]?.let { c ->
+            visited.add(this)
+            if (c == 9) 1
+            else neighbourCellsUDLR().filterNot { it in visited }
+                .filter { grid[it] == c + 1 }
+                .sumOf { it.score(visited) }
+        } ?: 0
     }
 
-
-    private fun Pos.score(visited: MutableSet<Pos>): Int {
-        visited.add(this)
-        val c = grid[this]!!
-        return if (c == 9) 1
-        else neighbourCellsUDLR().filterNot { it in visited }
-            .filter { it in grid }
-            .filter { grid[it] == c + 1 }
-            .sumOf { it.score(visited) }
+    private fun Pos.rating(path: List<Pos>, visited: MutableSet<List<Pos>>): Int {
+        return grid[this]?.let { c ->
+            val newPath = path + this
+            visited.add(newPath)
+            if (c == 9) 1
+            else neighbourCellsUDLR().filterNot { (newPath + it) in visited }
+                .filter { grid[it] == c + 1 }
+                .sumOf { it.rating(newPath, visited) }
+        } ?: 0
     }
 
     override fun List<String>.parse(): Map<Pos, Int> {