[PHP] 数据结构-反转链表PHP实现

1.常见方法分为迭代和递归,迭代是从头到尾,递归是从尾到头
2.设置两个指针,old和new,每一项添加在new的后面,新链表头指针指向新的链表头
3.old->next不能直接指向new,而是应该设置一个临时指针tmp,指向old->next指向的地址空间,保存原链表数据,然后old->next指向new,new往前移动到old处new=old,最后old=tmp取回数据
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
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}