light cleaning

src/day13.zig

@@ -14,15 +14,27 @@ const Solution = struct {
     b: usize,
 };
 
-fn findReflection(input: []const []const u8) usize {
+fn transpose(alloc: mem.Allocator, grid: []const []const u8) ![]const []const u8 {
+    std.debug.assert(grid.len > 0 and grid[0].len > 0);
+    var g = try alloc.alloc([]u8, grid[0].len);
+    for (0..grid[0].len) |i| {
+        g[i] = try alloc.alloc(u8, grid.len);
+    }
+    for (0..grid.len) |i| {
+        for (0..grid[i].len) |j| {
+            g[j][i] = grid[i][j];
+        }
+    }
+    return g;
+}
+
+fn findReflection(input: []const []const u8, err_tolerance: usize) ?usize {
     if (input.len == 0) return 0;
-    std.debug.print("{s}\n", .{input});
 
     const h = input.len;
     const w = input[0].len;
 
-    // Scan horizontal reflectivity
-    hscan: for (0..h - 1) |scan| {
+    for (0..h - 1) |scan| {
         var offset: usize = 0;
         var col: usize = 0;
         var errors: usize = 0;
@@ -30,42 +42,19 @@ fn findReflection(input: []const []const u8) usize {
             if (input[scan - offset][col] != input[scan + offset + 1][col]) {
                 errors += 1;
             }
-            if (errors > 1) {
-                continue :hscan;
+            if (errors > err_tolerance + 1) {
+                break;
             }
-            std.debug.print("{}±{} {} [{}]\n", .{ scan, offset, col, errors });
             col = (col + 1) % w;
             if (col == 0) offset += 1;
             if (scan < offset or scan + offset + 1 >= h) {
-                if (errors == 1) return (scan + 1) * 100;
-                continue :hscan;
+                if (errors == err_tolerance) return scan + 1;
+                break;
             }
         }
     }
 
-    // Scan vertical reflectivity
-    vscan: for (0..w - 1) |scan| {
-        var offset: usize = 0;
-        var row: usize = 0;
-        var errors: usize = 0;
-        while (true) {
-            if (input[row][scan - offset] != input[row][scan + offset + 1]) {
-                errors += 1;
-            }
-            if (errors > 1) {
-                continue :vscan;
-            }
-            std.debug.print("{} {}±{} [{}]\n", .{ row, scan, offset, errors });
-            row = (row + 1) % h;
-            if (row == 0) offset += 1;
-            if (scan < offset or scan + offset + 1 >= w) {
-                if (errors == 1) return scan + 1;
-                continue :vscan;
-            }
-        }
-    }
-
-    unreachable;
+    return null;
 }
 
 fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
@@ -73,20 +62,31 @@ fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
     defer curr_pattern.deinit();
 
     var it = util.splitLines(input);
-    var sum: usize = 0;
+    var sums = [2]usize{ 0, 0 };
     while (it.next()) |line| {
         if (line.len == 0) {
             const pattern = try curr_pattern.toOwnedSlice();
             defer alloc.free(pattern);
-            const score = findReflection(pattern);
-            std.debug.print("... {}\n", .{score});
-            sum += score;
+            for (0..2) |et| {
+                if (findReflection(pattern, et)) |score| {
+                    sums[et] += 100 * score;
+                } else {
+                    const t = try transpose(alloc, pattern);
+                    sums[et] += findReflection(t, et) orelse unreachable;
+
+                    // Ew.
+                    for (t) |r| {
+                        alloc.free(r);
+                    }
+                    alloc.free(t);
+                }
+            }
         } else {
             try curr_pattern.append(line);
         }
     }
 
-    return .{ .a = 405, .b = sum };
+    return .{ .a = sums[0], .b = sums[1] };
 }
 
 test "silver" {
@@ -108,9 +108,8 @@ test "silver" {
         \\#....#..#
         \\
     ;
-    _ = input;
-    // const sln = try solve(std.testing.allocator, input);
-    // try std.testing.expectEqual(@as(usize, 405), sln.a);
+    const sln = try solve(std.testing.allocator, input);
+    try std.testing.expectEqual(@as(usize, 405), sln.a);
 }
 
 test "gold" {