LeetCode 0036 - Valid Sudoku

class Solution {
private:
    bool book1[9][9] = {0};
    bool book2[9][9] = {0};
    bool book3[9][9] = {0};
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        for(int i = 0; i < 9; i++){
            for(int j = 0 ; j < 9; j++){
                if(board[i][j] != '.'){
                    int num = board[i][j] - '0' - 1;
                    int key = i / 3 * 3 + j / 3;
                    if(book1[i][num] || book2[j][num] || book3[key][num])
                        return 0;
                    book1[i][num] = book2[j][num] = book3[key][num] =1;
                }
            }
        }
        return 1;   
    }
};