[PHP] 數據結構-反轉鏈表PHP實現

1.常見方法分為迭代和遞歸,迭代是從頭到尾,遞歸是從尾到頭
2.設置兩個指針,old和new,每一項添加在new的后面,新鏈表頭指針指向新的鏈表頭
3.old->next不能直接指向new,而是應該設置一個臨時指針tmp,指向old->next指向的地址空間,保存原鏈表數據,然后old->next指向new,new往前移動到old處new=old,最后old=tmp取回數據
while(old!=null){
　　tmp=old->next
　　old->next=new
　　new=old
　　old=tmp
}

<?php
class Node{
        public $data;
        public $next;
}
//頭插法創建一個鏈表
$linkList=new Node();
$linkList->next=null;//頭結點
for($i=1;$i<=10;$i++){
        $node=new Node();
        $node->data="aaa{$i}";//創建新結點$node
        $node->next=$linkList->next;//$node->next指向頭結點->next
        $linkList->next=$node;//頭結點->next指向$node
}

var_dump($linkList);


function ReverseList($pHead){
        $old=$pHead->next;//跳過頭結點
        $new=null;
        $tmp=null;
        //反轉過程
        while($old!=null){
                $tmp=$old->next;
                $old->next=$new;
                $new=$old;
                $old=$tmp;
        }   
        //給新鏈表加個頭結點
        $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
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}