ZOHO QUESTION : Given a 9×9 sudoku we have to evaluate it for its correctness. We have to check both the sub matrix correctness and the whole sudoku correctness.

Discussion and Analysis:

Here is some interesting question we have about checking sudoku correctness.

Here the rules of sudoku following,

For example we have 9*9 sudoku,

So we have 81 number of square grid. This grid divided into 9 blocks.Each block have 9 square so totally 81 square.

So it has 9 rows and 9 columns. Each rows have number 1-9. But a number appears only once in the row as well as same rule for column.

Solution : 


/**
     * Find correctness.
     *
     * @return true, if successful
     */
    private static boolean evaluateSudoku() {
//Here is our input as 9*9 matrix.
        int[][] l_arrSudukoMatrix = new int[][] {
                { 5, 1, 3, 6, 8, 7, 2, 4, 9 },
                { 8, 4, 9, 5, 2, 1, 6, 3, 7 },
                { 2, 6, 7, 3, 4, 9, 5, 8, 1 },
                { 1, 5, 8, 4, 6, 3, 9, 7, 2 },
                { 9, 7, 4, 2, 1, 8, 3, 6, 5 },
                { 3, 2, 6, 7, 9, 5, 4, 1, 8 },
                { 7, 8, 2, 9, 3, 4, 1, 5, 6 },
                { 6, 3, 5, 1, 7, 2, 8, 9, 4 },
                { 4, 9, 1, 8, 5, 6, 7, 2, 3 } };
        Set<Integer> l_stRowSet = new HashSet<Integer>();
        Set<Integer> l_stColumnSet = new HashSet<Integer>();
//Here haveDuplicate variable to return the true/false. If haveDuplicate is false the sudoku is valid one.Otherwise its wrong sudoku.
        boolean haveDuplicate = true;

        for (int i = 0; i < l_arrSudukoMatrix.length; i++) {
            for (int j = 0; j < l_arrSudukoMatrix[i].length; j++) {
//Here to check the entered value is greater than zero and less than 10
              if(l_arrSudukoMatrix[i][j] > 0 && l_arrSudukoMatrix[i][j] < 10){
                l_stRowSet.add(l_arrSudukoMatrix[i][j]);
                }
            }
            for (int j = 0; j < l_arrSudukoMatrix[i].length; j++) {
//Here to check the entered value is greater than zero and less than 10
              if(l_arrSudukoMatrix[j][i] > 0 && l_arrSudukoMatrix[j][i] < 10){
                l_stColumnSet.add(l_arrSudukoMatrix[j][i]);
                }
            }
//If Row/Column have less than 9 size we have some repeated value, so we can return true.
            if (l_stRowSet.size() != 9 && l_stColumnSet.size() != 9) {
                return false;
            }
        }

        return haveDuplicate;

    }

Output : For this given input matrix true will be return.
If you modify some input with repeated value or greater than 9 and less than zero then system return false.


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