判断一个 9x9 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。上图是一个部分填充的有效的数独。
数独部分空格内已填入了数字，空白格用 '.' 表示。
示例 1:
输入:[ ["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:[ ["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。说明:
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。给定数独序列只包含数字 1-9 和字符 '.' 。给定数独永远是 9x9 形式的。解题思路
这个问题也非常简单，我们只需要判断上面说的三种情况是否都成立即可。我们可以通过一个数组记录出现的数字个数，最后统计这个数组中有没有数字个数>1的情况即可。
class Solution: def isValidSudoku(self, board): """ :type board: List[List[str]] :rtype: bool """ box1 = collections.defaultdict(int) box2 = collections.defaultdict(int) for i in range(9): for j in range(9): if board[i][j] != '.': box1[board[i][j]] += 1 if board[j][i] != '.': box2[board[j][i]] += 1 for v in box1.values(): if v > 1: return False for v in box2.values(): if v > 1: return False box1.clear() box2.clear() def square(x, y): nonlocal board box = collections.defaultdict(int) for i in range(3): for j in range(3): if board[i+x][j+y] != '.': box[board[i+x][j+y]] += 1 for v in box.values(): if v > 1: return False return True for i in range(0, 9, 3): for j in range(0, 9, 3): if not square(i, j): return False return True还有一个非常棒的思路就是，我们记录每行每列出现的数字，例如
对于col来说按照(行，数字)，对于row来说按照(数字，列)记录（注意数字是以字符的形式记录）。接着我们考虑如何记录小兴奋的吐司内的信息。我们采用这样的策略去记录(i//3,j//3,num)，这样对于左上角的兴奋的吐司就是(0,0,num)，对于右下角的兴奋的吐司就是(2,2,num)，其他兴奋的吐司同理。最后我们只要统计我们记录的元素中是不是有重复元素即可。
class Solution: def isValidSudoku(self, board): """ :type board: List[List[str]] :rtype: bool """ seen = [] for i, row in enumerate(board): for j, digit in enumerate(row): if digit != '.': seen.append((i, digit)) seen.append((digit, j)) seen.append((i // 3, j // 3, digit)) return len(seen) == len(set(seen))我将该问题的其他语言版本添加到了我的GitHub Leetcode
如有问题，希望大家指出！！！