PHP贪婪算法解决0-1背包问题实例分析

//0-1背包贪心算法问题
class tanxin{
public $weight;
public $price;
public function __construct($weight=0,$price=0)
{
$this->weight=$weight;
$this->price=$price;
}
}
//生成数据
$n=10;
for($i=1;$i<=$n;$i++){
$weight=rand(1,20);
$price=rand(1,10);
$x[$i]=new tanxin($weight,$price);
}
//输出结果
function display($x)
{
$len=count($x);
foreach($x as $val){
echo $val->weight,' ',$val->price;
echo '<br>';
}
}
//按照价格和重量比排序
function tsort(&$x)
{
$len=count($x);
for($i=1;$i<=$len;$i++)
{
for($j=1;$j<=$len-$i;$j++)
{
$temp=$x[$j];
$res=$x[$j+1]->price/$x[$j+1]->weight;
$temres=$temp->price/$temp->weight;
if($res>$temres){
$x[$j]=$x[$j+1];
$x[$j+1]=$temp;
}
}
}
}
//贪心算法
function tanxin($x,$totalweight=50)
{
$len=count($x);
$allprice=0;
for($i=1;$i<=$len;$i++){
if($x[$i]->weight>$totalweight) break;
else{
$allprice+=$x[$i]->price;
$totalweight=$totalweight-$x[$i]->weight;
}
}
if($i<$len) $allprice+=$x[$i]->price*($totalweight/$x[$i]->weight);
return $allprice;
}
tsort($x);//按非递增次序排序
display($x);//显示
echo '0-1背包最优解为:';
echo tanxin($x);