Unicorns VO 面试真题解析：判断 9 x 9 数独棋盘是否有效

Determine if a 9 x 9 Sudoku board is valid.

Only the filled cells need to be validated according to the following rules:

• Each row must contain the digits 1-9 without repetition.
• Each column must contain the digits 1-9 without repetition.
• Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

这道题要求判断一个 9 x 9 的数独棋盘是否合法，核心是检查已经填入的数字是否同时满足三类约束：每一行不能有重复数字、每一列不能有重复数字、每个 3 x 3 小宫格也不能重复。题目并不要求数独一定可解，只需要验证当前已填部分是否违反规则即可。实现时通常用哈希集合或布尔标记分别记录行、列和宫格中出现过的数字，遍历整个棋盘时一旦发现重复就直接返回 false，整体思路简单，适合用一次遍历完成。