|
9 | 9 | */
|
10 | 10 | public final class SudokuSolver {
|
11 | 11 |
|
12 |
| - private SudokuSolver() { |
13 |
| - } // Prevent instantiation |
| 12 | + private SudokuSolver() { |
| 13 | + } // Prevent instantiation |
14 | 14 |
|
15 |
| - /** |
16 |
| - * Solves the Sudoku puzzle using backtracking. |
17 |
| - * |
18 |
| - * @param sudoku 9x9 Sudoku grid, empty cells are 0 |
19 |
| - * @param row current row |
20 |
| - * @param col current column |
21 |
| - * @return true if solved, false otherwise |
22 |
| - */ |
23 |
| - public static boolean sudokuSolver(int[][] sudoku, int row, int col) { |
24 |
| - if (row == 9) { |
25 |
| - return true; |
26 |
| - } |
| 15 | + /** |
| 16 | + * Solves the Sudoku puzzle using backtracking. |
| 17 | + * |
| 18 | + * @param sudoku 9x9 Sudoku grid, empty cells are 0 |
| 19 | + * @param row current row |
| 20 | + * @param col current column |
| 21 | + * @return true if solved, false otherwise |
| 22 | + */ |
| 23 | + public static boolean sudokuSolver(int[][] sudoku, int row, int col) { |
| 24 | + if (row == 9) { |
| 25 | + return true; |
| 26 | + } |
27 | 27 |
|
28 |
| - int nextRow = row; |
29 |
| - int nextCol = col + 1; |
30 |
| - if (nextCol == 9) { |
31 |
| - nextRow = row + 1; |
32 |
| - nextCol = 0; |
33 |
| - } |
| 28 | + int nextRow = row; |
| 29 | + int nextCol = col + 1; |
| 30 | + if (nextCol == 9) { |
| 31 | + nextRow = row + 1; |
| 32 | + nextCol = 0; |
| 33 | + } |
34 | 34 |
|
35 |
| - if (sudoku[row][col] != 0) { |
36 |
| - return sudokuSolver(sudoku, nextRow, nextCol); |
37 |
| - } |
| 35 | + if (sudoku[row][col] != 0) { |
| 36 | + return sudokuSolver(sudoku, nextRow, nextCol); |
| 37 | + } |
38 | 38 |
|
39 |
| - for (int num = 1; num <= 9; num++) { |
40 |
| - if (isSafe(sudoku, row, col, num)) { |
41 |
| - sudoku[row][col] = num; |
42 |
| - if (sudokuSolver(sudoku, nextRow, nextCol)) { |
43 |
| - return true; |
44 |
| - } |
45 |
| - sudoku[row][col] = 0; // backtrack |
46 |
| - } |
| 39 | + for (int num = 1; num <= 9; num++) { |
| 40 | + if (isSafe(sudoku, row, col, num)) { |
| 41 | + sudoku[row][col] = num; |
| 42 | + if (sudokuSolver(sudoku, nextRow, nextCol)) { |
| 43 | + return true; |
| 44 | + } |
| 45 | + sudoku[row][col] = 0; // backtrack |
47 | 46 | }
|
| 47 | + } |
48 | 48 |
|
49 |
| - return false; |
50 |
| - } |
| 49 | + return false; |
| 50 | + } |
51 | 51 |
|
52 |
| - /** |
53 |
| - * Checks if placing num at (row, col) is safe. |
54 |
| - * |
55 |
| - * @param sudoku 9x9 Sudoku grid |
56 |
| - * @param row current row |
57 |
| - * @param col current column |
58 |
| - * @param num number to place |
59 |
| - * @return true if safe, false otherwise |
60 |
| - */ |
61 |
| - private static boolean isSafe(int[][] sudoku, int row, int col, int num) { |
62 |
| - for (int i = 0; i < 9; i++) { |
63 |
| - if (sudoku[row][i] == num || sudoku[i][col] == num) { |
64 |
| - return false; |
65 |
| - } |
| 52 | + /** |
| 53 | + * Checks if placing num at (row, col) is safe. |
| 54 | + * |
| 55 | + * @param sudoku 9x9 Sudoku grid |
| 56 | + * @param row current row |
| 57 | + * @param col current column |
| 58 | + * @param num number to place |
| 59 | + * @return true if safe, false otherwise |
| 60 | + */ |
| 61 | + private static boolean isSafe(int[][] sudoku, int row, int col, int num) { |
| 62 | + for (int i = 0; i < 9; i++) { |
| 63 | + if (sudoku[row][i] == num || sudoku[i][col] == num) { |
| 64 | + return false; |
66 | 65 | }
|
| 66 | + } |
67 | 67 |
|
68 |
| - int startRow = row - row % 3; |
69 |
| - int startCol = col - col % 3; |
70 |
| - for (int i = startRow; i < startRow + 3; i++) { |
71 |
| - for (int j = startCol; j < startCol + 3; j++) { |
72 |
| - if (sudoku[i][j] == num) { |
73 |
| - return false; |
74 |
| - } |
75 |
| - } |
| 68 | + int startRow = row - row % 3; |
| 69 | + int startCol = col - col % 3; |
| 70 | + for (int i = startRow; i < startRow + 3; i++) { |
| 71 | + for (int j = startCol; j < startCol + 3; j++) { |
| 72 | + if (sudoku[i][j] == num) { |
| 73 | + return false; |
| 74 | + } |
76 | 75 | }
|
| 76 | + } |
77 | 77 |
|
78 |
| - return true; |
79 |
| - } |
| 78 | + return true; |
| 79 | + } |
80 | 80 |
|
81 |
| - /** |
82 |
| - * Prints the Sudoku grid. |
83 |
| - * |
84 |
| - * @param sudoku 9x9 Sudoku grid |
85 |
| - */ |
86 |
| - public static void printSudoku(int[][] sudoku) { |
87 |
| - for (int i = 0; i < 9; i++) { |
88 |
| - for (int j = 0; j < 9; j++) { |
89 |
| - System.out.print(sudoku[i][j] + " "); |
90 |
| - } |
91 |
| - System.out.println(); |
| 81 | + /** |
| 82 | + * Prints the Sudoku grid. |
| 83 | + * |
| 84 | + * @param sudoku 9x9 Sudoku grid |
| 85 | + */ |
| 86 | + public static void printSudoku(int[][] sudoku) { |
| 87 | + for (int i = 0; i < 9; i++) { |
| 88 | + for (int j = 0; j < 9; j++) { |
| 89 | + System.out.print(sudoku[i][j] + " "); |
92 | 90 | }
|
93 |
| - } |
| 91 | + System.out.println(); |
| 92 | + } |
| 93 | + } |
94 | 94 | }
|
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