public boolean isValidSudoku(char[][] board){

HashMap<Integer,Integer> [] rows = new HashMap[9];

HashMap<Integer,Integer>[] cols = new HashMap[9];

HashMap<Integer,Integer>[] boxes = new HashMap[9];

for (int i = 0; i < 9; i++) {

rows[i] = new HashMap<Integer, Integer>();

cols[i] = new HashMap<Integer, Integer>();

boxes[i] = new HashMap<Integer, Integer>();

}

for (int i = 0; i < 9; i++) {

for (int j = 0; j < 9; j++) {

char num = board[i][j];

if (num != '.'){

int n = (int)num;

int box_index = (i/3)*3+j/3;

rows[i].put(n,rows[i].getOrDefault(n,0)+1);

cols[j].put(n,cols[j].getOrDefault(n,0)+1);

boxes[box_index].put(n,boxes[box_index].getOrDefault(n,0)+1);

if (rows[i].get(n) >1 || cols[j].get(n) >1 || boxes[box_index].get(n)>1){

return false;

}

}

}

}

return true;

}