Sudoku Solver

sudoku-solver.js

function sudoku(puzzle) {
  // returns the solved puzzle as a 2d array of 9 x 9
  const possibleValues = [1,2,3,4,5,6,7,8,9];
  let sections = [];
  // create array of values for 3x3 sections
  for (let i = 0; i < 9; i++) { sections.push([]); } 
  puzzle.forEach((row, rIndex) => {
    row.forEach((cell, cIndex) => {
      if (cell) { // ignore 0
        if (rIndex <= 2) {
          if (cIndex <= 2) { sections[0].push(cell); }
          else if (cIndex <= 5) { sections[1].push(cell); }
          else if (cIndex <= 8) { sections[2].push(cell); }
        } else if (rIndex <= 5) {
          if (cIndex <= 2) { sections[3].push(cell); }
          else if (cIndex <= 5) { sections[4].push(cell); }
          else if (cIndex <= 8) { sections[5].push(cell); }
        } else if (rIndex <= 8) {
          if (cIndex <= 2) { sections[6].push(cell); }
          else if (cIndex <= 5) { sections[7].push(cell); }
          else if (cIndex <= 8) { sections[8].push(cell); }
        }
      }
    });
  });
  //console.log('sections:', JSON.stringify(sections));
  // iterate puzzle and solve it
  while (sections.filter((val) => val.length < 9).length > 0) {
    for (let rIndex = 0, rMax = puzzle.length; rIndex < rMax; rIndex++) {
      for (let cIndex = 0, cMax = puzzle[rIndex].length; cIndex < cMax; cIndex++) {
        if (!puzzle[rIndex][cIndex]) {
          let square; // current section
          if (rIndex <= 2) {
            if (cIndex <= 2) { square = sections[0]; }
            else if (cIndex <= 5) { square = sections[1]; }
            else if (cIndex <= 8) { square = sections[2]; }
          } else if (rIndex <= 5) {
            if (cIndex <= 2) { square = sections[3]; }
            else if (cIndex <= 5) { square = sections[4]; }
            else if (cIndex <= 8) { square = sections[5]; }
          } else if (rIndex <= 8) {
            if (cIndex <= 2) { square = sections[6]; }
            else if (cIndex <= 5) { square = sections[7]; }
            else if (cIndex <= 8) { square = sections[8]; }
          }
          const squareMissing = possibleValues.filter((val) => square.indexOf(val) === -1);
          const rowMissing = possibleValues.filter((val, i) => puzzle[rIndex].indexOf(val) === -1);
          const columnPresent = puzzle.reduce((a, b) => { return (b[cIndex] !== 0) ? a.concat(b[cIndex]) : a }, []);
          const columnMissing = possibleValues.filter((val) => columnPresent.indexOf(val) === -1);
          /*
          console.log('squareMissing:', squareMissing);
          console.log('rowMissing:', rowMissing);
          console.log('columnPresent:', columnPresent);
          console.log('columnMissing:', columnMissing);
          */
          const options = squareMissing.filter((val) => rowMissing.indexOf(val) !== -1 && columnMissing.indexOf(val) !== -1);
          //console.log('options:', options);
          if (options.length === 1) {
            const option = options[0];
            if (squareMissing.indexOf(option) !== -1 && rowMissing.indexOf(option) !== -1 && columnMissing.indexOf(option) !== -1) {
              square.push(option);
              puzzle[rIndex][cIndex] = option;
            }
            //console.log('sections:', JSON.stringify(sections));
          }
        }
      }
    }
  }
  //console.log(puzzle);
  return puzzle;
}

SudokuSolver.markdown

Sudoku Solver

Solves 9x9 sudoku puzzles.

A script by V.

License.