day11 part2

src/day11.zig

@@ -44,7 +44,7 @@ fn findGaps(comptime T: type, alloc: mem.Allocator, occupied: std.AutoHashMap(T,
     return gaps.toOwnedSlice();
 }
 
-fn expand(comptime T: type, alloc: mem.Allocator, galaxies: []Point(T)) !void {
+fn expand(comptime T: type, alloc: mem.Allocator, galaxies: []Point(T), scale: T) !void {
     var seen_cols = std.AutoHashMap(T, void).init(alloc);
     defer seen_cols.deinit();
     var seen_rows = std.AutoHashMap(T, void).init(alloc);
@@ -60,21 +60,19 @@ fn expand(comptime T: type, alloc: mem.Allocator, galaxies: []Point(T)) !void {
     var gap_rows = try findGaps(T, alloc, seen_rows);
     defer alloc.free(gap_rows);
 
-    std.debug.print("expand x∋{any}, y∋{any}\n", .{ gap_cols, gap_rows });
-
     for (0..galaxies.len) |i| {
         const galaxy = galaxies[i];
 
         var col_offset: T = 0;
         for (gap_cols) |gap| {
             if (gap > galaxy.x) break;
-            col_offset += 1;
+            col_offset += scale - 1;
         }
 
         var row_offset: T = 0;
         for (gap_rows) |gap| {
             if (gap > galaxy.y) break;
-            row_offset += 1;
+            row_offset += scale - 1;
         }
 
         galaxies[i] = Point(T){ .x = galaxy.x + col_offset, .y = galaxy.y + row_offset };
@@ -85,7 +83,7 @@ fn absDiff(comptime T: type, a: T, b: T) T {
     return @max(a, b) - @min(a, b);
 }
 
-fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
+fn solvePart(alloc: mem.Allocator, input: []const u8, scale: usize) !usize {
     var galaxies = std.ArrayList(Point(usize)).init(alloc);
     defer galaxies.deinit();
 
@@ -105,7 +103,7 @@ fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
         y += 1;
     }
 
-    try expand(usize, alloc, galaxies.items);
+    try expand(usize, alloc, galaxies.items, scale);
 
     var distance: usize = 0;
     for (galaxies.items, 0..) |a, i| {
@@ -115,7 +113,11 @@ fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
         }
     }
 
-    return .{ .a = distance, .b = 0 };
+    return distance;
+}
+
+fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
+    return .{ .a = try solvePart(alloc, input, 2), .b = try solvePart(alloc, input, 1_000_000) };
 }
 
 test "silver" {
@@ -131,14 +133,23 @@ test "silver" {
         \\.......#..
         \\#...#.....
     ;
-    const sln = try solve(std.testing.allocator, input);
-    try std.testing.expectEqual(@as(usize, 374), sln.a);
+    const sln = try solvePart(std.testing.allocator, input, 2);
+    try std.testing.expectEqual(@as(usize, 374), sln);
 }
 
 test "gold" {
     const input =
-        \\
+        \\...#......
+        \\.......#..
+        \\#.........
+        \\..........
+        \\......#...
+        \\.#........
+        \\.........#
+        \\..........
+        \\.......#..
+        \\#...#.....
     ;
-    const sln = try solve(std.testing.allocator, input);
-    try std.testing.expectEqual(@as(usize, 0), sln.b);
+    try std.testing.expectEqual(@as(usize, 1030), try solvePart(std.testing.allocator, input, 10));
+    try std.testing.expectEqual(@as(usize, 8410), try solvePart(std.testing.allocator, input, 100));
 }