01背包问题实现探究

参考博文http://blog.csdn.net/mu399/article/details/7722810

另外bilibili有个讲背包01的视频也挺生动的。

<?php
//背包01问题
class Item{
    public $weight;
    public $value;
    public function __construct($weight,$value){
        $this->weight = $weight;
        $this->value = $value;
    }
}
class Bag{
    private $items;
    public function __construct($items){
        $this->items = $items;
    }
    private  $resultMap = array();
    function bestBag($k,$w){
        if($k==0 || $w==0){
            return 0;
        }
        if(isset($this->resultMap[$k][$w])){
            return $this->resultMap[$k][$w];
        }
        if($k==1) {
            if ($this->items[$k]->weight > $w) {
                return 0;
            } else {
                return $this->items[$k]->value;
            }
        }
        $res1 = $this->bestBag($k-1,$w);
        if($w-$this->items[$k]->weight>0){
            $res2 = $this->bestBag($k-1,$w-$this->items[$k]->weight)+$this->items[$k]->value;
        }else{
            $res2 = 0;
        }
        $result = max($res1,$res2);
        if(!isset($this->resultMap[$k][$w])){
            $this->resultMap[$k][$w] = $result;
        }
        return $result;
    }
}

$items = array();
for($i = 1;$i<6;$i++){
    $item = new Item($i,$i+3);
    $items[$i] = $item;
}
print_r($items);
$bagTest = new Bag($items);
echo $bagTest->bestBag(5,60);exit;