为什么在此php代码中出现致命错误：

Question

Getting the following error. Not sure why

Fatal error: Call to undefined function reverse_list_recursively()

<?php

class ListNode {
    public $data;
    public $next;

    function __construct($data) {
        $this->data = $data;
        $this->next = NULL;
    }

    function getData() {
        return $this->data;
    }
}

class LinkList {

    // points to the first node
    private $head;

    // node count
    private $count;

    function __construct() {
        $this->head = NULL;
        $this->count = 0;
    }

    // checks if the list is empty or not
    function is_empty() {
        return ($this->head == NULL);
    }

    // inserts data at the beginning of the list
    public function insert_beg($data) {

        $link = new ListNode($data);
        $link->next = $this->head;
        $this->head = &$link;
        $this->count++;
    }

    public function insert_last($data) {
        $current = $this->head;

        if($current == NULL) {
           $this->insert_beg($data);

        } else {

            while($current->next != NULL) {
                $current = $current->next;
            }
            $link = new ListNode($data);
            $current->next = &$link;
            $link->next = NULL;
            $this->count++;
        }
    }

    public function delete_first_node() {
        if($this->head != NULL) {
            if($this->head->next != NULL) {
                $this->head = $this->head->next;
                $this->count--;
            }
        }
    }

    public function delete_last_node() {

        $current = $this->head;
        if($current != NULL) {

            $prev = $current;
            while($current->next != NULL) {
                $prev = $current;
                $current = $current->next;
            }
            $current = $prev;
            $current->next = NULL;
            $this->count--;
        }
    }

    public function delete_node($data) {
        $current = $prev = $this->head;
        if ($current == NULL) {
            return;
        } else {
            while($current->data != $data && $current->next != NULL) {
                $prev = $current;
                $current = $current->next;
            }
            if($current->data == $data) {
                $prev->next = $current->next;
                $this->count--;
            }
            return;
        }
    }

    public function reverse_list_iteratively() {
        $current = $this->head;

        // if the list is empty or only one element in the list return
        if($current == NULL || $current->next == NULL) {
            return;
        } else {
            $next = $prev = NULL;
            while($current != NULL) {
                $next = $current->next;
                $current->next = $prev;
                $prev = $current;
                $current = $next;

            }
            $this->head = $prev;
        }
    }

    public function reverse_list_recursively($current = NULL) {
        $current = $this->head;

        // base case when the current is empty
        if($current->next == NULL) {
            $this->head = $current;
            return $current;
        } else {
            reverse_list_recursively($current->next);
            $current->next->next = $current;
            $current->next = NULL;
        }

    }

    public function print_list() {
        $current = $this->head;
        echo "\nThe list is: ";
        while($current != NULL) {
            echo "$current->data" . " ";
            $current = $current->next;
        }
    }

    public function get_size() {
        return $this->count;
    }

}
    $totalNodes = 10;

    $list = new LinkList();


    echo "Is list empty before adding nodes: ";
    var_export($list->is_empty());
    echo "\n";

    for($i=1; $i <= $totalNodes; $i++) {
        $list->insert_last($i);
    }

    echo "Is list empty after adding nodes: "; 
    var_export( $list->is_empty());
    echo "\n";

    echo "Size of the list: " .  $list->get_size();
    echo "\n";

    echo "List is: ";
    $list->print_list();
    echo "\n";


    echo "Deleting first node: ";
    $list->delete_first_node();
    $list->print_list();
    echo "\n";

    echo "Deleting last node: ";
    $list->delete_last_node();
    $list->print_list();
    echo "\n";

    echo "Deleting node 6: ";
    $list->delete_node(6);
    $list->print_list();
    echo "\n";

    echo "Reversing the list iteratively";
    $list->reverse_list_iteratively();
    $list->print_list();
    echo "\n";

    echo "Reversing the list rec";
    $list->reverse_list_recursively();
    $list->print_list();
    echo "\n";



?>

Answer 1

You can access same class function using $this keyword

at line 131 replace

reverse_list_iteratively($current->next);

with

$this->reverse_list_iteratively($current->next);

Explanation

reverse_list_iteratively() is a class function(and its not static), so you need object to access this function, for same class you can access with $ this keyword

Answer 2

your call is done with no parameter:

$list->reverse_list_recursively();

and your definition takes 1 parameter:

public function reverse_list_recursively($current = NULL)

I am suspecting that this could be issue.

Answer 3

in this case you have defined the function with an argument but you are passing nothing so it is finding the argument. you can try this

echo "Reversing the list rec";
$list->reverse_list_recursively(0);
$list->print_list();
echo "\n";