题目：https://leetcode-cn.com/problems/valid-sudoku/
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。
分析：
1.判断值存不存在可以使用HashSet;
2.每行、每列、每3x3 宫可以单独放在一个HashSet中判断数值是否重复；
代码：
public boolean isValidSudoku(char[][] board) { HashSet[] row = new HashSet[9]; HashSet[] column = new HashSet[9]; HashSet[] box = new HashSet[9]; for (int i=0;i<9;i++){ row[i] = new HashSet(9); column[i] = new HashSet(9); box[i] = new HashSet(9); } for (int i=0;i<9;i++){ for (int j=0;j<9;j++){ if (board[i][j]==‘.‘){ continue; } if (row[i].contains(board[i][j])){ return false; } if (column[j].contains(board[i][j])){ return false; } int boxIndex = i/3*3 + j/3; if (box[boxIndex].contains(board[i][j])){ return false; } row[i].add(board[i][j]); column[j].add(board[i][j]); box[boxIndex].add(board[i][j]); } } return true; }
原文：https://www.cnblogs.com/guaniu2750/p/12814858.html