Determine if a Sudoku is valid, according to: .
The Sudoku board could be partially filled, where empty cells are filled with the character'.'.
A partially filled sudoku which is valid.
Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.
思路：按照规则，先检查行，然后检查列，然后检查9格。
public class Solution { public boolean isValidSudoku(char[][] board) { int i; for (i = 0; i < 9; i++) { if (!isValid(board, i, i + 1, 0, 9)) return false; } int j; for (j = 0; j < 9; j++) { if (!isValid(board, 0, 9, j, j + 1)) return false; } for (i = 0; i < 9; i = i + 3) for (j = 0; j < 9; j = j + 3) { if (!isValid(board, i, i + 3, j, j + 3)) return false; } return true; } private boolean isValid(char[][] board, int iBegin, int iEnd, int jBegin, int jEnd) { HashSet set = new HashSet (); for (int i = iBegin; i < iEnd; i++) for (int j = jBegin; j < jEnd; j++) { if (set.contains(board[i][j])) return false; else if (board[i][j] != '.') set.add(board[i][j]); } return true; } public static void main(String[] args) { char[][] 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' } }; System.out.println(new Solution().isValidSudoku(board)); }}