Valid Sudoku

描述​

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules http://sudoku.com.au/TheRules.aspx .

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

代码​

// Valid Sudoku// 时间复杂度O(n^2)，空间复杂度O(1)public class Solution {    public boolean isValidSudoku(char[][] board) {        boolean[] used = new boolean[9];        for (int i = 0; i < 9; ++i) {            Arrays.fill(used, false);            for (int j = 0; j < 9; ++j) // 检查行                if (!check(board[i][j], used))                    return false;            Arrays.fill(used, false);            for (int j = 0; j < 9; ++j) // 检查列                if (!check(board[j][i], used))                    return false;        }        for (int r = 0; r < 3; ++r) // 检查 9 个子格子            for (int c = 0; c < 3; ++c) {                Arrays.fill(used, false);                for (int i = r * 3; i < r * 3 + 3; ++i)                    for (int j = c * 3; j < c * 3 + 3; ++j)                        if (!check(board[i][j], used))                            return false;            }        return true;    }    private static boolean check(char ch, boolean[] used) {        if (ch == '.') return true;        if (used[ch - '1']) return false;        return used[ch - '1'] = true;    }};