Valid Sudoku

use three 2-d matrix to store if any column, row or block has more than one specific value.

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        boolean[][] rows = new boolean[9][9];
        boolean[][] cols = new boolean[9][9];
        boolean[][] blocks = new boolean[9][9];

        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                if (board[i][j] == '.') continue;
                int c = board[i][j] - '1';
                if (rows[i][c] || cols[j][c] || blocks[i - i % 3 + j / 3][c])
                    return false;
                rows[i][c] = cols[j][c] = blocks[i - i % 3 + j / 3][c] = true;
            }
        }
        return true;
    }
}