php 优先队列实现（堆实现，简单版本）

# basic node format of Heap

class HeapNode {

    var $value;

}

# the format of this Heap's node should like the
# class HeapNode:contain $value to compare

class Heap {

    var $flag; // true:queue from small to big;   false:from big to small
    var $array; // the array for saving nodes

    #constructor of this class

    function Heap($param = true) {
        global $flag;
        $flag = $param;
    }

    #push node into array, no length limit

    function push($node) {
        global $array;
        if (empty($array)) {
            $array = array($node);
        } else {
            array_push($array, $node);
        }
        $idx = count($array) - 1;
        // push in the last position, than adjust from bottom to top
        while ($this->cmp($array[$idx], $array[($idx - 1) / 2])) {
            $this->swap($array[$idx], $array[($idx - 1) / 2]);
            $idx = ($idx - 1) / 2;
        }
    }

    #pop the min/max node, return success:true/fail:false

    function pop() {
        global $array;

        if (empty($array)) { // pop empty heap, return fail
            return false;
        }
        changeLastToRoot();
        if (empty($array)) { // no element, finish this function
            return true;
        }
        adjustRootNode();
        return true;
    }

    # pop the first element and change the last one to the root position

    function changeLastToRoot() {
        global $array;
        $length = count($array);
        $array[0] = $array[$length - 1];
        array_pop($array);
    }

    function adjustRootNode() {
        global $array;
        $curNode = $array[0]; // record the node need to adjust
        $parent = 0; // begin from root
        if (empty($array)) {
            $length = 0;
        } else {
            $length = count($array);
        }
        for ($i = $parent * 2 + 1; $i < $length; $i*=2) {
            if ($i < $length - 1 and $this->cmp($array[$i + 1], $array[$i])) {
                $i++;
            }

            if ($this->cmp($curNode, $array[$i])) {
                break;
            }
            $array[$parent] = $array[$i];
            $parent = $i;
        }
        $array[$parent] = $curNode;
    }

    # return the min/max node, if no element return null

    function top() {
        global $array;
        if (empty($array)) {
            return null;
        } else {
            return $array[0];
        }
    }

    # judge array whether has element

    function isEmpty() {
        global $array;
        return empty($array);
    }

    #judging that how to compare

    protected function cmp($node1, $node2) {
        global $flag;
        if ($flag) {
            return $node1->value < $node2->value;
        } else {
            return $node1->value > $node2->value;
        }
    }

    protected function swap(&$node1, &$node2) {
        $tmp = $node1;
        $node1 = $node2;
        $node2 = $tmp;
    }

}