2024/day 06 - part 2

Author: underlow

src/main/kotlin/me/underlow/advent2024/Day06.kt

@@ -51,12 +51,12 @@ object GuardGallivant {
             if (list[next.row][next.col] != '#') {
                 start = next
                 visited += start
-                println("${visited.size} Step to $start")
+//                println("${visited.size} Step to $start")
                 continue
             }
 
             dir = dir.rotateRight()
-            println("Rotate to $dir")
+//            println("Rotate to $dir")
         }
 
 
@@ -65,7 +65,94 @@ object GuardGallivant {
 
     fun part2(list: List<String>): Int {
         val directions = parseInput(list)
-        return 0
+
+        var start: Point? = null
+        var dir: Dir? = null
+        for (i in list.indices) {
+            for (j in list[0].indices)
+                when {
+                    list[i][j] == '^' -> {
+                        start = Point(i, j)
+                        dir = Dir.Up
+                    }
+
+                    list[i][j] == '>' -> {
+                        start = Point(i, j)
+                        dir = Dir.Right
+                    }
+
+                    list[i][j] == 'v' -> {
+                        start = Point(i, j)
+                        dir = Dir.Down
+                    }
+
+                    list[i][j] == '<' -> {
+                        start = Point(i, j)
+                        dir = Dir.Left
+                    }
+                }
+        }
+
+        var sum = 0
+
+        for (i in list.indices) {
+            for (j in list[0].indices) {
+                if (i == start!!.col && j == start.row) {
+                    continue
+                }
+                if (directions[i][j] == '#') {
+                    continue
+                }
+
+                val saved = directions[i][j]
+                directions[i][j] = '#'
+//                println("Try: $i $j")
+                sum += if (loop(start, directions, dir)) 1 else 0
+
+                directions[i][j] = saved
+
+
+            }
+        }
+
+        return sum
+    }
+
+    private fun loop(
+        start: Point?,
+        list: Array<Array<Char>>,
+        dir: Dir?
+    ): Boolean {
+        var start1 = start
+        var dir1 = dir
+        val visited = mutableSetOf<Pair<Point, Dir>>()
+        visited += (start1!! to dir1!!)
+
+        while (start1!!.row in list.indices && start1.col in list[0].indices) {
+            //make a step
+            val next = start1.move(dir1!!)
+
+            if ((next to dir1) in visited) {
+                // loop
+//                println("Loop: $next to $dir of $visited")
+                return true
+            }
+
+            if (!(next.row in list.indices && next.col in list[0].indices)) {
+                break
+            }
+
+            if (list[next.row][next.col] != '#') {
+                start1 = next
+                visited += start1 to dir1
+//                println("${visited.size} Step to $start1")
+                continue
+            }
+
+            dir1 = dir1.rotateRight()
+//            println("Rotate to $dir1")
+        }
+        return false
     }
 
     private fun parseInput(list: List<String>): Array<Array<Char>> {
@@ -80,7 +167,7 @@ fun main() {
     val res2 = GuardGallivant.part2(input)
 
     checkResult(res1, 4722)
-    checkResult(res2, 0)
+    checkResult(res2, 1602)
 
     println(res1)
     println(res2)

src/test/kotlin/me/underlow/advent2024/GuardGallivantTest.kt

@@ -11,7 +11,7 @@ class GuardGallivantTest {
     @Test
     fun testPart2() {
         val result = GuardGallivant.part2(input.split("\n"))
-        assertEquals(0, result)
+        assertEquals(6, result)
     }
 }