请你判断一个 9 x 9 的数独是否有效。只需要 根据以下规则 ，验证已经填入的数字是否有效即可。
数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）注意：
一个有效的数独（部分已被填充）不一定是可解的。
只需要根据以上规则，验证已经填入的数字是否有效即可。
空白格用 '.' 表示。
示例 1：
输入：board = | |
[["5","3",".",".","7",".",".",".","."] | |
,["6",".",".","1","9","5",".",".","."] | |
,[".","9","8",".",".",".",".","6","."] | |
,["8",".",".",".","6",".",".",".","3"] | |
,["4",".",".","8",".","3",".",".","1"] | |
,["7",".",".",".","2",".",".",".","6"] | |
,[".","6",".",".",".",".","2","8","."] | |
,[".",".",".","4","1","9",".",".","5"] | |
,[".",".",".",".","8",".",".","7","9"]] | |
输出：true |
示例 2：
输入：board = | |
[["8","3",".",".","7",".",".",".","."] | |
,["6",".",".","1","9","5",".",".","."] | |
,[".","9","8",".",".",".",".","6","."] | |
,["8",".",".",".","6",".",".",".","3"] | |
,["4",".",".","8",".","3",".",".","1"] | |
,["7",".",".",".","2",".",".",".","6"] | |
,[".","6",".",".",".",".","2","8","."] | |
,[".",".",".","4","1","9",".",".","5"] | |
,[".",".",".",".","8",".",".","7","9"]] | |
输出：false | |
解释：除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。 但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。 |
提示：
board.length == 9 | |
board[i].length == 9 | |
board[i][j] 是一位数字（1-9）或者 '.' |
题解
public boolean isValidSudoku(char[][] board) { | |
int length = board[0].length; | |
int[][] line = new int[9][9]; | |
int[][] column = new int[9][9]; | |
int[][][] triangle = new int[3][3][9]; | |
for (int i = 0; i < length; i++){ | |
for (int j = 0; j < length; j++){ | |
// 当前字符 | |
char c = board[i][j]; | |
// 当为。时，不统计 | |
if ('.' == c) continue; | |
// 当前数字 | |
int index = c - '0' - 1; | |
// 统计该行当前数字出现的个数 | |
line[i][index]++; | |
// 统计该列当前数字出现的个数 | |
column[j][index]++; | |
// 统计 3*3 方格里当前数字出现的个数 | |
triangle[i/3][j/3][index]++; | |
// 如果 > 1，则是无效数独 | |
if (line[i][index] > 1 || column[j][index] > 1 || triangle[i/3][j/3][index] > 1) return false; | |
} | |
} | |
return true; | |
} |
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/valid-sudoku
