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// Package godoku is a simple, brute-force,
// in-place sudoku solver
package godoku
import (
"bytes"
"fmt"
"io/ioutil"
"strconv"
"strings"
)
type Sudoku struct {
board Board
solved bool
solutionCount int
doPrint bool
dim int
solveAll bool
solution Board
}
type Board [][]int
func (s *Sudoku) PrintBoard() {
for _, row := range s.board {
fmt.Println(row)
}
}
// IsValidBoard iterates through all initial
// values on the board and verifies that they indeed
// abide by the 3 laws of Sudoku
func (s *Sudoku) IsValidBoard() bool {
if s.board == nil {
return false
}
for i, row := range s.board {
for j, val := range row {
if val == 0 {
continue
}
s.board[i][j] = 0
if !s.ValidValueAtPosition(i, j, val) {
s.board[i][j] = val
return false
}
s.board[i][j] = val
}
}
return true
}
// String returns either the unsolved board if the
// sudoku has not been solved, or the solution
// if such a solution has been found
// by running one of the Solve* methods.
func (s *Sudoku) String() string {
var buffer bytes.Buffer
if s.solved {
for _, row := range s.solution {
buffer.WriteString(fmt.Sprintf("%v\n", row))
}
return buffer.String()
}
for _, row := range s.board {
buffer.WriteString(fmt.Sprintf("%v\n", row))
}
return buffer.String()
}
// GetSolution returns the solution
// BUG(paddie): doesn't check if board is solved
func (s *Sudoku) GetSolution() Board {
return s.solution
}
// Load a sudoku from a path and a dimension argument
func NewSudokuFromFile(path string, dim int) (*Sudoku, error) {
s := new(Sudoku)
var err error
s.board, err = readBoardFromFile(path, dim)
if err != nil {
return nil, err
}
s.dim = dim
return s, nil
}
// Loads a sudoku-board in a string-representation;
// The values are in a 9x9 matrix, using space " " as delimiters and '\n' as linebreaks
func NewSudokuFromString(path string, dim int) (*Sudoku, error) {
s := new(Sudoku)
var err error
s.board, err = readBoardFromString(path, dim)
if err != nil {
return nil, err
}
s.dim = dim
return s, nil
}
/*
Returns the number of solutions found.
*/
func (s *Sudoku) GetSolutionsCount() int {
return s.solutionCount
}
// registers the first solutions in the s.solution
// board, and prints if doPrint is set.
func (s *Sudoku) registerSolution() {
s.solutionCount++
if s.doPrint {
s.PrintBoard()
}
if s.solved {
return
}
s.solved = true
s.solution = make(Board, 9, 9)
for i, row := range s.board {
s.solution[i] = make([]int, 9, 9)
copy(s.solution[i], row)
}
}
// Check if the solver has found a solution
func (s *Sudoku) IsSolved() bool {
return s.solved
}
// The dimensions of the sudoku board
func (s *Sudoku) Dimension() int {
return s.dim
}
// Solve and save the solution. Returns an error if no Sudoku has been loaded
func (s *Sudoku) Solve() error {
s.solved = false
if s.board == nil {
return fmt.Errorf("No Board has been loaded..")
}
s.solveAll = false
s.bruteforcePosition(0, 0)
return nil
}
// Same as Solve(), but this one also prints
// the solution to stdin
func (s *Sudoku) SolveAndPrint() error {
s.doPrint = true
err := s.Solve()
s.doPrint = false
return err
}
// Same as Solve, but keeps running until it has all
// the solutions and keeps a count. It only saves the first solution
func (s *Sudoku) SolveAll() error {
s.solved = false
if s.board == nil {
return fmt.Errorf("No Board has been loaded..")
}
s.solveAll = true
s.bruteforcePosition(0, 0)
return nil
}
// Same as SolveAll but prints all the solutions
// to stdin
func (s *Sudoku) SolveAllAndPrint() error {
s.doPrint = true
err := s.SolveAll()
s.doPrint = false
return err
}
func (s *Sudoku) bruteforcePosition(row, col int) {
// we use '0' to indicate a non-filled block
if s.board[row][col] == 0 {
for i := 1; i < 10; i++ {
if s.ValidValueAtPosition(row, col, i) {
// place the value and attempt to solve
s.board[row][col] = i
// attempt to solve the sudoku with placed value
s.nextPosition(row, col)
if s.solved && !s.solveAll {
// if Solve() was used, we break
// after first solution
s.board[row][col] = 0
return
}
// clean up after attempt
s.board[row][col] = 0
}
}
} else {
s.nextPosition(row, col)
}
}
// Does two things:
//
// 1) if the board is in a finished state, calls
// registerSolution() and returns;
// enables bruteforcePostion to exhaust every remaining permutation
//
// 2) checks wether to move to next column or next row
func (s *Sudoku) nextPosition(row, col int) {
// we run through the Board row by row
// meaning we only change rows when we're in
// the final column
if col < 8 {
s.bruteforcePosition(row, col+1)
} else {
// if we're in the final collumn in the final
// row; we have a solution
// - else we iterate to next row and reset the collumn
if row < 8 {
s.bruteforcePosition(row+1, 0)
} else {
s.registerSolution()
}
}
}
// Verify that _val_ can be legally placed at (row,col)
// given restrictions in column, row and 3x3 square
func (s *Sudoku) ValidValueAtPosition(row, col, val int) bool {
if s.ValidInSquare(row, col, val) &&
s.ValidInColumnAndRow(row, col, val) {
// validInRow(row, val, Board) {
return true
}
return false
}
// Checks that the _val_ does not already occur in the
// active 3x3 square
func (s *Sudoku) ValidInSquare(row, col, val int) bool {
row, col = int(row/3)*3, int(col/3)*3
for i := row; i < row+3; i++ {
for j := col; j < col+3; j++ {
//fmt.Printf("row, col = %v, %v\n", i, j)
if s.board[i][j] == val {
return false
}
}
}
return true
}
// Checks if _val_ already occurs in either the row or the column.
func (s *Sudoku) ValidInColumnAndRow(row, col, val int) bool {
for i := 0; i < 9; i++ {
if s.board[row][i] == val ||
s.board[i][col] == val {
return false
}
}
return true
}
func readBoardFromFile(path string, dim int) (Board, error) {
content, err := ioutil.ReadFile(path)
if err != nil {
return nil, err
}
return readBoardFromString(string(content), dim)
}
func readBoardFromString(m string, dim int) (Board, error) {
lines := strings.Split(m, "\n")
if len(lines) < dim {
return nil, fmt.Errorf("row count of input: %v does not match dim: %v", len(lines), dim)
}
Board := make(Board, dim, dim)
for i := 0; i < dim; i++ {
stringRows := strings.Split(lines[i], " ")
if len(stringRows) < dim {
return nil, fmt.Errorf("column count of input: %v does not match dim: %v", len(lines[i]), dim)
}
integerRow := make([]int, dim, dim)
for j := 0; j < dim; j++ {
str := stringRows[j]
val, err := strconv.Atoi(str)
if err != nil {
return nil, err
}
integerRow[j] = val
}
Board[i] = integerRow
}
return Board, nil
}
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