algorithmpool/src/algopool/sets/sudokuSolver.js

A pool of algorithms and data-structures for geeks

const UNASSIGNED = 0;

function usedInRow(matrix, row, num) {
    for (let col = 0; col < matrix.length; col++) {
        if (matrix[row][col] === num) {
            return true;
        }
    }
    return false;
}

function usedInCol(matrix, col, num) {
    for (let row = 0; row < matrix.length; row++) {
        if (matrix[row][col] === num) {
            return true;
        }
    }
    return false;
}

function usedInBox(matrix, boxStartRow, boxStartCol, num) {
    for (let row = 0; row < 3; row++) {
        for (let col = 0; col < 3; col++) {
            if (matrix[row + boxStartRow][col + boxStartCol] === num) {
                return true;
            }
        }
    }
    return false;
}

function isSafe(matrix, row, col, num) {
    return (
        !usedInRow(matrix, row, num) &&
        !usedInCol(matrix, col, num) &&
        !usedInBox(matrix, row - (row % 3), col - (col % 3), num)
    );
}

function solveSudoku(matrix) {
    let row = 0;
    let col = 0;
    let checkBlankSpaces = false;

    for (row = 0; row < matrix.length; row++) {
        for (col = 0; col < matrix[row].length; col++) {
            if (matrix[row][col] === UNASSIGNED) {
                checkBlankSpaces = true;
                break;
            }
        }
        if (checkBlankSpaces === true) {
            break;
        }
    }
    if (checkBlankSpaces === false) {
        return true;
    }

    for (let num = 1; num <= 9; num++) {
        if (isSafe(matrix, row, col, num)) {
            matrix[row][col] = num;
            if (solveSudoku(matrix)) {
                return true;
            }
            matrix[row][col] = UNASSIGNED;
        }
    }
    return false;
}

export const sudokuSolver = (matrix) => {
    if (solveSudoku(matrix) === true) {
        return matrix;
    }
    return 'NO SOLUTION EXISTS!';
}