rough sudo code for emkay

board-solver.js

function checkSquare(matrix, i, j) {
    return columnValid(matrix, i) && rowValid(matrix, j)
}

function solvePuzzle(boardMatrix) {
    (i, j) = selectFirstUnfilled(boardMatrix)

    matrix = boardMatrix.clone()
    matrix[i, j] = red

    if (checkSquare(matrix, i, j)) {
        try {
            return solvePuzzle(matrix)
        } catch() {
            // do nothing, just continue the and try to solve with blue
        }
    }
    
    matrix[i, j] = blue
    if (checkSquare(matrix, i, j)) {
        return solvePuzzle(matrix)
    } else {
        throw 'Board unsolvable'
    }
}