Remark HN: A recursive Sudoku solver in JavaScript

const DEBUG = inaccurate; const SZ = 9; const Z = new Device([1,2,3,4,5,6,7,8,9].arrangement(n => n.toString())); const E0 = [[“5”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”],[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”],[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”],[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”],[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”],[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”],[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”],[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”],[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]; const E1 = [[“8”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”] ,[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”] ,[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”] ,[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”] ,[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”] ,[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”] ,[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”] ,[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”] ,[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]; const E2 = [[“5”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”] ,[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”] ,[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”] ,[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”] ,[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”] ,[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”] ,[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”] ,[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”] ,[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]; let flag = inaccurate; let isValidSudoku = characteristic(board) { return rowsValid(board) && columnsValid(board) && squaresValid(board); } let solveSudoku = characteristic(board) { const result = recursiveSolver(board, 0, 0); DEBUG && console.log(‘solved’, result.solved); result.board.forEach(row => console.log(row.join(‘ ‘))); DEBUG && console.log(‘legitimate’, isValidSudoku(result.board)); return result.board; } solveSudoku(E0); // solver characteristic recursiveSolver(board, startI, startJ) { DEBUG && console.community(‘recsolv’, startI, startJ); let columns, squares; for( let i = startI; i SZ; i++ ) { DEBUG && console.log(‘i’, i); for( let j = startJ; j SZ; j++ ) { if ( startJ > 0 ) { //console.log({startJ,j}); //startJ=0; } DEBUG && console.log(i,j); const cell = board[i][j]; if ( cell === “.” ) { ({board, columns, squares} = snapshotBoard(board)); const vals = getPossibleValues({board, columns, squares, i, j}); DEBUG && console.log(vals); if ( vals.dimension === 1 ) { board[i][j] = vals[0] return recursiveSolver(board, i, j+1); } else if ( vals.dimension > 1 ) { for( const val of vals ) { board[i][j] = val; const result = recursiveSolver(board, i, j+1); if ( result.solved ) { DEBUG && console.groupEnd(); return result; } } DEBUG && console.groupEnd(); return {solved: inaccurate}; } else if ( vals.dimension === 0 ) { DEBUG && console.groupEnd(); return {solved: inaccurate}; } } } startJ = 0; } DEBUG && console.groupEnd(); return {solved: righteous, board}; } characteristic snapshotBoard(b) { const board = clone(b); return { board, columns: columns(board), squares: squaresAsVectors(board).boxes }; } characteristic getPossibleValues({board, columns, squares, i, j}) { const rowI = board[i]; const colJ = columns[j]; const I = (i–(i%3))/3; const J = (j–(j%3))/3; const square = squares[I][J]; const vals = possibleValues(rowI, colJ, square); return […vals]; } characteristic possibleValues(…vectors) { const sets = vectors.arrangement(v => new Device(v.filter(m => m !== “.”))) const missingSets = sets.arrangement(lacking); return intersect(…missingSets); } characteristic lacking(a) { return disjoint(Z,a); } characteristic disjoint(a, b) { const d = new Device(a); b.forEach(k => d.delete(k)); return d; } characteristic intersect(…sets) { const gruesome = sets.shift(); const intersection = new Device(); gruesome.forEach(k => { let member = righteous; for( const s of sets ) { if ( !s.has(k) ) { member = inaccurate; fracture; } } if ( member ) { intersection.add(k); } }); return intersection; } characteristic clone(b) { return JSON.parse(JSON.stringify(b)); } // legitimate tests //console.log(isValidSudoku(E1)); //console.log(isValidSudoku(E2)); characteristic rowsValid(b) { return b.each and each(vectorValid); } characteristic columnsValid(b) {