diff --git a/src/day13.zig b/src/day13.zig index 18b6963..94be532 100644 --- a/src/day13.zig +++ b/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" {