1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
const SudokuSolver = struct {
const countEql = std.simd.countElementsWithValue;
const join = std.simd.join;
// Each cell exists in memory three times.
// This makes it easy to compare a guess against all relevant cells simultaneously.
rows: [9]@Vector(9, u8),
cols: [9]@Vector(9, u8),
boxes: [9]@Vector(9, u8),
fn init(board: [9][9]u8) !SudokuSolver {
var res: SudokuSolver = .{
.rows = undefined,
.cols = undefined,
.boxes = undefined,
};
for (0..9) |row| {
for (0..9) |col| {
const cell = board[row][col];
if (cell > 9) return error.InvalidValue;
res.setCell(row, col, cell);
}
}
return res;
}
fn possibleMovesForCell(self: SudokuSolver, row: usize, col: usize) std.StaticBitSet(9) {
var cell_guesses: std.StaticBitSet(9) = .initEmpty();
for (1..10) |n| {
// A number is a possible move iff it does not already exist in the current row, col, or box.
if (countEql(
join(self.rows[row], join(self.cols[col], self.boxes[boxOf(row, col)])),
@intCast(n),
) == 0) {
cell_guesses.set(n - 1);
}
}
return cell_guesses;
}
fn solveEasyBoard(self: *SudokuSolver) !void {
while (!self.isSolved()) {
var moved_this_iteration = false;
for (self.rows, 0..) |row, row_i| {
for (@as([9]u8, row), 0..) |cell, col_i| {
if (cell == 0) {
const possible_moves = self.possibleMovesForCell(row_i, col_i);
if (possible_moves.count() == 1) {
self.setCell(
row_i,
col_i,
@intCast(possible_moves.findFirstSet().? + 1),
);
moved_this_iteration = true;
}
}
}
}
if (!moved_this_iteration) return error.UnableToSolve;
}
}
fn isSolved(self: SudokuSolver) bool {
for (self.rows) |row| {
if (countEql(row, 0) > 0) return false;
}
return true;
}
fn setCell(self: *SudokuSolver, row: usize, col: usize, value: u8) void {
self.rows[row][col] = value;
self.cols[col][row] = value;
self.boxes[boxOf(row, col)][cellOfInBox(row, col)] = value;
}
fn boxOf(row: usize, col: usize) usize {
// Due to integer division, this is not the same as just adding row.
return (row / 3) * 3 + col / 3;
}
fn cellOfInBox(row: usize, col: usize) usize {
return (row % 3) * 3 + col % 3;
}
fn display(self: SudokuSolver, writer: std.io.AnyWriter) !void {
for (self.rows, 0..) |row, i| {
// Can't loop over row directly?
for (@as([9]u8, row), 0..) |cell, j| {
try writer.print("{d} ", .{cell});
if (j % 3 == 2 and j < 8) {
try writer.print("| ", .{});
}
}
try writer.print("\n", .{});
if (i % 3 == 2 and i < 8) {
try writer.print("{s}\n", .{"-" ** 21});
}
}
}
};
pub fn main() !void {
var board: [9][9]u8 = undefined;
const stdout = std.io.getStdOut().writer().any();
const stdin = std.io.getStdIn().reader().any();
for (0..9) |row| {
for (0..9) |col| {
const byte = try stdin.readByte();
board[row][col] = try std.fmt.charToDigit(byte, 10);
}
}
// Unreachable because we validate while parsing.
var solver = SudokuSolver.init(board) catch unreachable;
solver.solveEasyBoard() catch |err| {
std.debug.print("Unable to solve board\n", .{});
return err;
};
try solver.display(stdout);
}
const std = @import("std");
test "boxOf" {
const expectEql = std.testing.expectEqual;
try expectEql(0, SudokuSolver.boxOf(0, 0));
try expectEql(1, SudokuSolver.boxOf(0, 3));
try expectEql(2, SudokuSolver.boxOf(2, 8));
try expectEql(4, SudokuSolver.boxOf(4, 5));
}
test "cellOfInBox" {
const expectEql = std.testing.expectEqual;
try expectEql(0, SudokuSolver.cellOfInBox(0, 0));
try expectEql(1, SudokuSolver.cellOfInBox(0, 1));
try expectEql(2, SudokuSolver.cellOfInBox(0, 2));
try expectEql(3, SudokuSolver.cellOfInBox(1, 0));
try expectEql(0, SudokuSolver.cellOfInBox(3, 3));
try expectEql(0, SudokuSolver.cellOfInBox(6, 6));
}
test "get available moves for easy board" {
// Taken from https://ziggit.dev/t/i-wrote-a-simple-sudoku-solver/9924/14?u=zambyte
if (false) {
const board: [9][9]u8 = .{
.{ 4, 0, 3, 5, 0, 0, 0, 9, 6 },
.{ 5, 0, 7, 8, 0, 0, 3, 0, 0 },
.{ 0, 8, 0, 0, 0, 0, 0, 5, 4 },
.{ 0, 0, 0, 7, 0, 6, 0, 2, 3 },
.{ 0, 0, 0, 0, 2, 0, 0, 0, 0 },
.{ 9, 5, 0, 3, 0, 4, 0, 0, 0 },
.{ 7, 9, 0, 0, 0, 0, 0, 6, 0 },
.{ 0, 0, 4, 0, 0, 7, 5, 0, 8 },
.{ 8, 3, 0, 0, 0, 5, 4, 0, 9 },
};
const solver: SudokuSolver = SudokuSolver.init(.{ .board = board }) catch unreachable;
for (board, 0..) |row, row_i| {
for (row, 0..) |cell, col_i| {
if (cell == 0) {
const possible_moves = solver.possibleMovesForCell(row_i, col_i);
if (possible_moves.count() == 1) {
std.debug.print("row: {}, col: {}, value: {}\n", .{ row_i, col_i, possible_moves.findFirstSet().? });
}
}
}
}
}
return error.SkipZigTest;
}
test "Solve easy board" {
// Taken from https://ziggit.dev/t/i-wrote-a-simple-sudoku-solver/9924/14?u=zambyte
const board: [9][9]u8 = .{
.{ 4, 0, 3, 5, 0, 0, 0, 9, 6 },
.{ 5, 0, 7, 8, 0, 0, 3, 0, 0 },
.{ 0, 8, 0, 0, 0, 0, 0, 5, 4 },
.{ 0, 0, 0, 7, 0, 6, 0, 2, 3 },
.{ 0, 0, 0, 0, 2, 0, 0, 0, 0 },
.{ 9, 5, 0, 3, 0, 4, 0, 0, 0 },
.{ 7, 9, 0, 0, 0, 0, 0, 6, 0 },
.{ 0, 0, 4, 0, 0, 7, 5, 0, 8 },
.{ 8, 3, 0, 0, 0, 5, 4, 0, 9 },
};
var solver: SudokuSolver = SudokuSolver.init(board) catch unreachable;
const stderr = std.io.getStdErr().writer().any();
std.debug.print("input:\n", .{});
try solver.display(stderr);
std.debug.print("output:\n", .{});
try solver.solveEasyBoard();
try solver.display(stderr);
}
|
