Sudoku.js

class Sudoku {
 // Sudoku Class to hold the board and related functions
 constructor (board) {
 this.board = board
 }

 findEmptyCell () {
 // Find a empty cell in the board (returns [-1, -1] if all cells are filled)
 for (let i = 0; i < 9; i++) {
 for (let j = 0; j < 9; j++) {
 if (this.board[i][j] === 0) return [i, j]
 }
 }
 return [-1, -1]
 }

 check ([y, x], value) {
 // checks if the value to be added in the board is an acceptable value for the cell

 // checking through the row
 for (let i = 0; i < 9; i++) {
 if (this.board[i][x] === value) return false
 }
 // checking through the column
 for (let i = 0; i < 9; i++) {
 if (this.board[y][i] === value) return false
 }

 // checking through the 3x3 block of the cell
 const secRow = Math.floor(y / 3)
 const secCol = Math.floor(x / 3)
 for (let i = (secRow * 3); i < ((secRow * 3) + 3); i++) {
 for (let j = (secCol * 3); j < ((secCol * 3) + 3); j++) {
 if (y !== i && x !== j && this.board[i][j] === value) return false
 }
 }

 return true
 }

 solve () {
 const [y, x] = this.findEmptyCell()

 // checking if the board is complete
 if (y === -1 && x === -1) return true

 for (let val = 1; val < 10; val++) {
 if (this.check([y, x], val)) {
 this.board[y][x] = val
 if (this.solve()) return true
 // backtracking if the board cannot be solved using current configuration
 this.board[y][x] = 0
 }
 }
 // returning false the board cannot be solved using current configuration
 return false
 }

 getSection (row, [start, end]) {
 return this.board[row].slice(start, end)
 }

 printBoard (output = (...v) => console.log(...v)) {
 // helper function to display board
 for (let i = 0; i < 9; i++) {
 if (i % 3 === 0 && i !== 0) {
 output('- - - - - - - - - - - -')
 }
 output(
 ...this.getSection(i, [0, 3]), ' | ',
 ...this.getSection(i, [3, 6]), ' | ',
 ...this.getSection(i, [6, 9]))
 }
 }
}

export { Sudoku }