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| 1 | +class Solution { |
| 2 | + public function __construct() { |
| 3 | + $this->row = array_fill(0, 9, array_fill(0, 9, false)); |
| 4 | + $this->col = array_fill(0, 9, array_fill(0, 9, false)); |
| 5 | + $this->grid = array_fill(0, 9, array_fill(0, 9, false)); |
| 6 | + $this->found = false; |
| 7 | + } |
| 8 | + |
| 9 | + /** |
| 10 | + * @param String[][] $board |
| 11 | + * @return NULL |
| 12 | + */ |
| 13 | + function solveSudoku(&$board) { |
| 14 | + for ($i = 0; $i < 9; ++$i) { |
| 15 | + for ($j = 0; $j < 9; ++$j) { |
| 16 | + if ($board[$i][$j] != '.') { |
| 17 | + $this->row[$i][ord($board[$i][$j]) - ord('1')] = true; |
| 18 | + $this->col[$j][ord($board[$i][$j]) - ord('1')] = true; |
| 19 | + $this->grid[intval(($i / 3)) * 3 + intval(($j / 3)) % 3][ord($board[$i][$j]) - ord('1')] = true; |
| 20 | + } |
| 21 | + } |
| 22 | + } |
| 23 | + self::place(0, $board); |
| 24 | + return; |
| 25 | + } |
| 26 | + function place($n, &$board) { |
| 27 | + if ($n == 81) { |
| 28 | + // board = g; |
| 29 | + $this->found = true; |
| 30 | + return; |
| 31 | + } |
| 32 | + |
| 33 | + $i = intval($n / 9); $j = $n % 9; |
| 34 | + $index = intval(($i / 3)) * 3 + intval(($j / 3)) % 3; |
| 35 | + if ($board[$i][$j] == '.') { |
| 36 | + for ($c = 0; $c < 9; ++$c) { |
| 37 | + if (!$this->row[$i][$c] && !$this->col[$j][$c] && !$this->grid[$index][$c]) { |
| 38 | + $this->row[$i][$c] = true; |
| 39 | + $this->col[$j][$c] = true; |
| 40 | + $this->grid[$index][$c] = true; |
| 41 | + $board[$i][$j] = chr($c + ord('1')); |
| 42 | + |
| 43 | + self::place($n + 1, $board); |
| 44 | + |
| 45 | + if ($this->found) |
| 46 | + return; |
| 47 | + |
| 48 | + $board[$i][$j] = '.'; |
| 49 | + $this->row[$i][$c] = false; |
| 50 | + $this->col[$j][$c] = false; |
| 51 | + $this->grid[$index][$c] = false; |
| 52 | + |
| 53 | + } |
| 54 | + } |
| 55 | + } |
| 56 | + else |
| 57 | + self::place($n + 1, $board); |
| 58 | + return; |
| 59 | + } |
| 60 | +} |
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