leetcode36：valid sudoku

public boolean isValidSudoku(char[][] board) {
for (int i=0; i<9; i++) {
if (!isParticallyValid(board,i,0,i,8)) return false;
if (!isParticallyValid(board,0,i,8,i)) return false;
}
for (int i=0;i<3;i++){
for(int j=0;j<3;j++){
if (!isParticallyValid(board,i*3,j*3,i*3+2,j*3+2)) return false;
}
}
return true;
}
private boolean isParticallyValid(char[][] board, int x1, int y1,int x2,int y2){
Set singleSet = new HashSet();
for (int i= x1; i<=x2; i++){
for (int j=y1;j<=y2; j++){
if (board[i][j]!='.') if(!singleSet.add(board[i][j])) return false;
}
}
return true;
}