PHP 逆轉單鏈表

 1 <?php 2     #逆轉單鏈表 3     class Node { 4         public $data = null; 5         public $next = null; 6     } 7  8     #遞迴版本 9     #思想是一直遞迴到倒數第二個非空節點，並將其next->next指向自己，將自己的next指向null10     #為了獲得逆轉後的頭結點，在最後一個非空節點，即cnode->next == null時，將節點返回11     function reverse_list_r($node) {12         if ($node->next == null) {13             return $node;14         } else {15             $head = reverse_list_r($node->next);16             $node->next->next = $node;17             $node->next = null;18             return $head;19         }20     }21 22     #非遞迴版本23     #思想是需要儲存下三個節點，分別是cnode,next(cnode->next),next2(cnode->next->next)24     #每次要執行的操作只有將next->next指向cnode，然後依次將這三個節點後移，直到next == null25     function reverse_list($head) {26         $cnode = $head;27         $next = $head->next;28         $head->next = null;29         while ($next != null) {30             $next2 = $next->next;31             $next->next = $cnode; 32             $cnode = $next;33             $next = $next2;34         }35 36         return $cnode;37     }38 39     #遍曆單鏈表40     function traverse($head) {41         $cnode = $head;42         while ($cnode != null) {43             echo $cnode->data . " ";44             $cnode = $cnode->next;45         }46         echo "<br>";47     }48 49     $head = new Node();50     $n1 = new Node();51     $n2 = new Node();52     $n3 = new Node();53     $head->data = 0;54     $n1->data = 1;55     $n2->data = 2;56     $n3->data = 3;57     $head->next = $n1;58     $n1->next = $n2;59     $n2->next = $n3;60     $n3->next = null;61     traverse($head);62 63     $rhead = reverse_list_r($head);64     traverse($rhead);65 66     $rrhead = reverse_list($rhead);67     traverse($rrhead);68 ?>

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