Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.
The Sudoku board could be partially filled, where empty cells are filled with
the character ‘.‘.
A partially filled sudoku which is valid.
Here is a brute force method. I do not whether there is an other smart method.
1 public class Solution{ 2 public boolean isValidSudoku(char[][] board) { 3 boolean isValid = true; 4 HashSet<Character> column = new HashSet<Character>(); 5 HashSet<Character> row = new HashSet<Character>(); 6 for(int i = 0; i < 9; ++i){ 7 //clear the set, before we insert into a new row or column 8 column.clear(); 9 row.clear(); 10 for(int j = 0; j < 9; ++j){ 11 if(board[i][j] != ‘.‘) 12 isValid = isValid && row.add(board[i][j]); 13 if(board[j][i] != ‘.‘) 14 isValid = isValid && column.add(board[j][i]); 15 if(!isValid) 16 break; 17 } 18 if(!isValid) 19 break; 20 } 21 if(isValid){ 22 HashSet<Character> square = new HashSet<Character>(); 23 int i = 0; 24 while(i < 9){ 25 int j = 0; 26 while(j < 9){ 27 square.clear(); 28 for(int ii = 0; ii < 3; ++ii){ 29 for(int jj = 0; jj < 3; ++jj){ 30 if(board[i +ii][j + jj] != ‘.‘) 31 isValid = square.add(board[i +ii][j + jj]); 32 if(!isValid) 33 return false; 34 } 35 } 36 j += 3; 37 } 38 i += 3; 39 } 40 } 41 return isValid; 42 } 43 }