Detaillierte Erklärung, wie man Sudoku in PHP löst

<?php
/* 数独求解程序
 *
 */
 class Sudoku {
  var $matrix;
  function __construct($arr = null) {
    if ($arr == null) {
      $this->clear();
    } else {
      $this->matrix = $arr;
    }
  }
  function clear() {
    for($i=0; $i<9; $i++) {
      for($j=0; $j<9; $j++) {
        $this->matrix[$i][$j] = array();
        for ($k = 1; $k <= 9; $k++) {
          $this->matrix[$i][$j][$k] = $k;
        }
      }
    }
  }
  function setCell($row, $col, $value){
    $this->matrix[$row][$col] = array($value => $value);
    //row
    for($i = 0; $i < 9; $i++){
      if($i != $col){
        if(! $this->removeValue($row, $i, $value)) {
          return false;
        }
      }
    }
    //col
    for($i = 0; $i < 9; $i++){
      if($i != $row){
        if(! $this->removeValue($i, $col, $value)) {
          return false;
        }
      }
    }
    //square
    $rs=intval($row / 3) * 3;
    $cs=intval($col / 3) * 3;
    for($i = $rs; $i < $rs + 3; $i++){
      for($j = $cs; $j < $cs + 3; $j++){
        if($i != $row && $j != $col){
          if(! $this->removeValue($i, $j, $value))
            return false;
        }
      }
    }
    return true;
  }
  function removeValue($row, $col, $value) {
    $count = count($this->matrix[$row][$col]);
    if($count == 1){
      $ret = !isset($this->matrix[$row][$col][$value]);
      return $ret;
    }
    if (isset($this->matrix[$row][$col][$value])) {
      unset($this->matrix[$row][$col][$value]);
      if($count - 1 == 1) {
        return $this->setCell($row, $col, current($this->matrix[$row][$col]));
      }
    }
    return true;
  }
  function set($arr) {
    for ($i = 0; $i < 9; $i++) {
      for ($j = 0; $j < 9; $j++) {
        if ($arr[$i][$j] > 0) {
          $this->setCell($i, $j, $arr[$i][$j]);
        }
      }
    }
  }
  function dump() {
    for($i = 0; $i < 9; $i++){
      for($j = 0; $j < 9; $j++){
        $c = count($this->matrix[$i][$j]);
        if($c == 1){
          echo " ".current($this->matrix[$i][$j])." ";
        } else {
          echo "(".$c.")";
        }
      }
      echo "\n";
    }
    echo "\n";
  }
  function dumpAll() {
    for($i = 0; $i < 9; $i++){
      for($j = 0; $j < 9; $j++){
        echo implode(&#39;&#39;, $this->matrix[$i][$j]), "\t";
      }
      echo "\n";
    }
    echo "\n";
  }
  function calc($data) {
    $this->clear();
    $this->set($data);
    $this->_calc();
    $this->dump();
  }
  function _calc() {
    for($i = 0; $i < 9; $i++){
      for($j = 0; $j < 9; $j++){
        if(count($this->matrix[$i][$j]) == 1) {
          continue;
        }
        foreach($this->matrix[$i][$j] as $v){
          $flag = false;
          $t = new Sudoku($this->matrix);
          if(!$t->setCell($i, $j, $v)){
            continue;
          }
          if(!$t->_calc()){
            continue;
          }
          $this->matrix = $t->matrix;
          return true;
        }
        return false;
      }
    }
    return true;
  }
}
$sd=new Sudoku;
$sd->calc(array(
array(0,5,0,0,0,6,0,9,0),
array(0,4,7,0,8,2,6,0,0),
array(0,8,0,0,0,7,0,5,2),
array(7,0,1,0,3,4,0,0,6),
array(0,3,0,0,2,0,0,8,0),
array(2,0,0,0,0,1,9,0,4),
array(4,7,0,1,0,0,0,6,0),
array(0,0,9,4,6,0,3,7,0),
array(0,1,0,2,0,0,0,4,0),
));
$sd->calc(array(
array(1,0,0,0,0,6,9,0,0),
array(0,0,0,9,0,0,0,0,5),
array(2,0,0,1,0,0,0,0,3),
array(0,0,5,3,0,7,0,2,0),
array(3,0,0,6,0,0,0,0,1),
array(0,1,0,4,0,0,8,0,0),
array(9,0,0,0,0,2,0,0,7),
array(5,0,0,0,0,9,0,0,0),
array(0,0,3,7,0,0,0,0,4),
));
$sd->calc(array(
array(7,0,0,1,0,0,0,0,5),
array(0,0,6,0,4,0,0,8,0),
array(0,0,1,0,0,0,0,0,0),
array(0,6,0,0,8,0,0,0,3),
array(0,8,0,0,0,9,0,7,0),
array(1,0,0,0,0,0,0,5,0),
array(0,0,0,0,0,0,9,0,0),
array(0,4,0,0,3,0,1,0,0),
array(9,0,0,0,0,7,0,0,2),
));
$sd->calc(array(
array(0,5,0,0,0,0,0,2,0),
array(0,0,3,1,0,0,5,0,0),
array(0,0,6,0,0,8,0,0,0),
array(6,0,0,0,0,0,0,1,0),
array(8,0,0,6,0,0,0,0,4),
array(0,3,0,0,0,9,0,0,7),
array(0,0,0,5,0,0,3,0,0),
array(0,0,8,0,0,6,9,0,0),
array(0,9,0,0,0,0,0,7,0),
));
?>

 1 5 2 3 4 6 7 9 8 
 9 4 7 5 8 2 6 1 3 
 3 8 6 9 1 7 4 5 2 
 7 9 1 8 3 4 5 2 6 
 5 3 4 6 2 9 1 8 7 
 2 6 8 7 5 1 9 3 4 
 4 7 3 1 9 8 2 6 5 
 8 2 9 4 6 5 3 7 1 
 6 1 5 2 7 3 8 4 9 

 1 3 7 2 5 6 9 4 8 
 4 6 8 9 7 3 2 1 5 
 2 5 9 1 8 4 6 7 3 
 6 8 5 3 1 7 4 2 9 
 3 9 4 6 2 8 7 5 1 
 7 1 2 4 9 5 8 3 6 
 9 4 6 5 3 2 1 8 7 
 5 7 1 8 4 9 3 6 2 
 8 2 3 7 6 1 5 9 4 

 7 3 8 1 9 6 4 2 5 
 2 9 6 3 4 5 7 8 1 
 4 5 1 2 7 8 3 9 6 
 5 6 9 7 8 4 2 1 3 
 3 8 2 5 1 9 6 7 4 
 1 7 4 6 2 3 8 5 9 
 6 2 7 4 5 1 9 3 8 
 8 4 5 9 3 2 1 6 7 
 9 1 3 8 6 7 5 4 2 

 9 5 1 3 6 7 4 2 8 
 7 8 3 1 4 2 5 6 9 
 2 4 6 9 5 8 7 3 1 
 6 2 9 4 7 5 8 1 3 
 8 7 5 6 1 3 2 9 4 
 1 3 4 2 8 9 6 5 7 
 4 6 7 5 9 1 3 8 2 
 3 1 8 7 2 6 9 4 5 
 5 9 2 8 3 4 1 7 6