sudoku2.js

//Turn columns into rows
var transpose = grid =>
    grid[0].map(
        (_,c) => grid.map(
            row => row[c]
        )
    )

//Turn sub-grids into rows
var expandSubGrids = grid => {
    var three = Math.sqrt(grid.length);
    return grid[0].map(
        (_,i) => grid[0].map(
            (_,j) => grid[(i/three|0)*three+j/three|0][i%three*three+j%three]
        )
    )
}

//Check a given row for duplicates
var checkRow = row => {
    var count = [];
    for(var cell of row) {
        if(cell != '.') {
            if(count[cell])
                return false;
            count[cell] = 1;
        }
    }
    return true;
}

var sudoku2 = grid =>
    grid.every(checkRow) &&
    transpose(grid).every(checkRow) &&
    expandSubGrids(grid).every(checkRow)

sudoku2.txt

Sudoku is a number-placement puzzle. The objective is to fill a 9 × 9 grid with numbers in such a way that each column, each row, and each of the nine 3 × 3 sub-grids that compose the grid all contain all of the numbers from 1 to 9 one time.

Implement an algorithm that will check whether the given grid of numbers represents a valid Sudoku puzzle according to the layout rules described above. Note that the puzzle represented by grid does not have to be solvable.

Example

For

grid = [['.', '.', '.', '1', '4', '.', '.', '2', '.'],
        ['.', '.', '6', '.', '.', '.', '.', '.', '.'],
        ['.', '.', '.', '.', '.', '.', '.', '.', '.'],
        ['.', '.', '1', '.', '.', '.', '.', '.', '.'],
        ['.', '6', '7', '.', '.', '.', '.', '.', '9'],
        ['.', '.', '.', '.', '.', '.', '8', '1', '.'],
        ['.', '3', '.', '.', '.', '.', '.', '.', '6'],
        ['.', '.', '.', '.', '.', '7', '.', '.', '.'],
        ['.', '.', '.', '5', '.', '.', '.', '7', '.']]
the output should be
sudoku2(grid) = true;

For

grid = [['.', '.', '.', '.', '2', '.', '.', '9', '.'],
        ['.', '.', '.', '.', '6', '.', '.', '.', '.'],
        ['7', '1', '.', '.', '7', '5', '.', '.', '.'],
        ['.', '7', '.', '.', '.', '.', '.', '.', '.'],
        ['.', '.', '.', '.', '8', '3', '.', '.', '.'],
        ['.', '.', '8', '.', '.', '7', '.', '6', '.'],
        ['.', '.', '.', '.', '.', '2', '.', '.', '.'],
        ['.', '1', '.', '2', '.', '.', '.', '.', '.'],
        ['.', '2', '.', '.', '3', '.', '.', '.', '.']]
the output should be
sudoku2(grid) = false.

The given grid is not correct because there are two 1s in the second column. Each column, each row, and each 3 × 3 subgrid can only contain the numbers 1 through 9 one time.

Input/Output

[execution time limit] 4 seconds (js)

[input] array.array.char grid

A 9 × 9 array of characters, in which each character is either a digit from '1' to '9' or a period '.'.

[output] boolean

Return true if grid represents a valid Sudoku puzzle, otherwise return false.

[JavaScript (ES6)] Syntax Tips

// Prints help message to the console
// Returns a string
function helloWorld(name) {
    console.log("This prints to the console when you Run Tests");
    return "Hello, " + name;
}