aoc2024

commit 1caf5cea2cc5120fd45f78b483398777c8227c2e
parent 961570ce442e0d98a9fe1e6a1966354d7096ea07
Author: Martin Ashby <martin@ashbysoft.com>
Date:   Tue, 31 Dec 2024 21:25:36 +0000

Day 10 pt2

Diffstat:
A
src/main/java/day10_pt2.java
 | 
53
+++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 53 insertions(+), 0 deletions(-)
diff --git a/src/main/java/day10_pt2.java b/src/main/java/day10_pt2.java
@@ -0,0 +1,53 @@
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.io.IOException;
+import java.util.*;
+import java.util.stream.*;
+
+public class day10_pt2 {
+  record Point(int x, int y) {
+    Point add(Vec v) {
+      return new Point(this.x + v.x, this.y + v.y);
+    }
+  }
+  record Vec(int x, int y) {}
+  private static final Vec[] DIRS = new Vec[]{new Vec( 0, 1),
+                                              new Vec( 1, 0),
+                                              new Vec( 0,-1),
+                                              new Vec(-1, 0)};
+  public static void main(String[] args) throws IOException {
+    var grid = Files.readAllLines(Path.of(args[0]));
+    var trailheads = new ArrayList<Point>();
+    var height = grid.size();
+    var width = grid.get(0).length();
+    // pass 1 find trailheads
+    for (int y=0; y<height; y++) {
+      for (int x=0; x<width; x++) {
+        var val = gv(grid, new Point(x, y));
+        if (val == 0) {
+          trailheads.add(new Point(x, y));
+        }
+      }
+    }
+    var res = trailheads.stream().mapToInt(th -> rating(grid, th)).sum();
+    System.out.printf("Day 10, pt2: %d\n", res);
+  }
+  
+  static int gv(List<String> grid, Point p) {
+    if (p.y < 0 || p.y >= grid.size()) return -1;
+    if (p.x < 0 || p.x >= grid.get(0).length()) return -1;
+    return grid.get(p.y).charAt(p.x) - '0';
+  }
+
+  static int rating(List<String> grid, Point p) {
+    var val = gv(grid, p);
+    if (val == 9) {
+      return 1;
+    } else {
+      return Arrays.stream(DIRS)
+        .filter(d -> gv(grid, p.add(d)) == val+1)
+        .mapToInt(d -> rating(grid, p.add(d)))
+        .sum();
+    }
+  }
+}