sudoku | 数独ソルバー

def strassen(matrix1: list, matrix2: list) -> list:
    """
    >>> strassen([[2,1,3],[3,4,6],[1,4,2],[7,6,7]], [[4,2,3,4],[2,1,1,1],[8,6,4,2]])
    [[34, 23, 19, 15], [68, 46, 37, 28], [28, 18, 15, 12], [96, 62, 55, 48]]
    >>>  

public static boolean solveSudoku(
            int[][] board, int n) {
        int row = -1;
        int col = -1;
        boolean isEmpty = true;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                i  

private static boolean isValidSudoku(char[][] board) {
        HashSet[] nums = new HashSet[9];
        for (int i = 0; i < 9; i++) {
            nums[i] = new HashSet<>(Arrays.asList('1', '2', '3', '4', '5', '6', '7', '8', '9'));
        }