How to reverse linked list in php (code example)

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1. Common methods are divided into iteration and recursion. Iteration is from beginning to end, and recursion is from end to beginning.
2. Set two pointers, old and new, and add each item after new. The new linked list head pointer points to the new linked list head
3. old->next cannot directly point to new, but a temporary pointer tmp should be set to point to the address space pointed by old->next, save the original linked list data, and then old->next points to new, new moves forward to old, new=old, and finally old=tmp retrieves the data

while(old!=null){
　　tmp=old->next
　　old->next=new
　　new=old
　　old=tmp
}

<?php
class Node{
        public $data;
        public $next;
}
//头插法创建一个链表
$linkList=new Node();
$linkList->next=null;//头结点
for($i=1;$i<=10;$i++){
        $node=new Node();
        $node->data="aaa{$i}";//创建新结点$node
        $node->next=$linkList->next;//$node->next指向头结点->next
        $linkList->next=$node;//头结点->next指向$node
}

var_dump($linkList);


function ReverseList($pHead){
        $old=$pHead->next;//跳过头结点
        $new=null;
        $tmp=null;
        //反转过程
        while($old!=null){
                $tmp=$old->next;
                $old->next=$new;
                $new=$old;
                $old=$tmp;
        }   
        //给新链表加个头结点
        $newHead=new Node();
        $newHead->next=$new;
        var_dump($newHead);
}
ReverseList($linkList);

object(Node)#1 (2) {
  ["data"]=>
  NULL
  ["next"]=>
  object(Node)#11 (2) {
    ["data"]=>
    string(5) "aaa10"
    ["next"]=>
    object(Node)#10 (2) {
      ["data"]=>
      string(4) "aaa9"
      ["next"]=>
      object(Node)#9 (2) {
        ["data"]=>
        string(4) "aaa8"
        ["next"]=>
        object(Node)#8 (2) {
          ["data"]=>
          string(4) "aaa7"
          ["next"]=>
          object(Node)#7 (2) {
            ["data"]=>
            string(4) "aaa6"
            ["next"]=>
            object(Node)#6 (2) {
              ["data"]=>
              string(4) "aaa5"
              ["next"]=>
              object(Node)#5 (2) {
                ["data"]=>
                string(4) "aaa4"
                ["next"]=>
                object(Node)#4 (2) {
                  ["data"]=>
                  string(4) "aaa3"
                  ["next"]=>
                  object(Node)#3 (2) {
                    ["data"]=>
                    string(4) "aaa2"
                    ["next"]=>
                    object(Node)#2 (2) {
                      ["data"]=>
                      string(4) "aaa1"
                      ["next"]=>
                      NULL
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}
object(Node)#12 (2) {
  ["data"]=>
  NULL
  ["next"]=>
  object(Node)#2 (2) {
    ["data"]=>
    string(4) "aaa1"
    ["next"]=>
    object(Node)#3 (2) {
      ["data"]=>
      string(4) "aaa2"
      ["next"]=>
      object(Node)#4 (2) {
        ["data"]=>
        string(4) "aaa3"
        ["next"]=>
        object(Node)#5 (2) {
          ["data"]=>
          string(4) "aaa4"
          ["next"]=>
          object(Node)#6 (2) {
            ["data"]=>
            string(4) "aaa5"
            ["next"]=>
            object(Node)#7 (2) {
              ["data"]=>
              string(4) "aaa6"
              ["next"]=>
              object(Node)#8 (2) {
                ["data"]=>
                string(4) "aaa7"
                ["next"]=>
                object(Node)#9 (2) {
                  ["data"]=>
                  string(4) "aaa8"
                  ["next"]=>
                  object(Node)#10 (2) {
                    ["data"]=>
                    string(4) "aaa9"
                    ["next"]=>
                    object(Node)#11 (2) {
                      ["data"]=>
                      string(5) "aaa10"
                      ["next"]=>
                      NULL
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

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