PHP 链表结构之环型链表（三）

php链表结构 环型链表（三）

环型链表结构，我们这边的环型链表其实和双向链表相似，就是最后一个节点指向了我们的开始节点上，我们这边定义一个节点类，属性有当前值(data)和指向下一个节点的(next)， 和指向上一个节点的（previous）。

class Node {
    public $data;
    public $next;
    public $previous;

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

之后是链表结构类 ，我们定义一个头节点，以头节点开始，next指向下一个节点，previous指向上一个节点，具体看情况添加你所需要的其他属性，并且将最后一个节点的next指向第一个节点

class LoopLinkedList
{
    private $headList;

    public function __construct($data)
    {
        $this->headList = new Node($data);
        $this->headList->next = $this->headList;
        $this->headList->previous = $this->headList;
    }
}

1. 往链表中插入一个值(尾部插入)

public function insert($data) {
    $currentNode = $this->headList;
    while ($currentNode->next !== $this->headList) {
        $currentNode = $currentNode->next;
    }
    $newNode = new Node($data);
    $currentNode->next = $newNode;
    $newNode->previous = $currentNode;
    $newNode->next = $this->headList;
    $this->headList->previous = $newNode;
}
$loop_link = new LoopLinkedList(1);
$loop_link->insert(2);
$loop_link->insert(3);
var_dump($loop_link);
结果：
object(LoopLinkedList)#1 (1) {
  ["headList":"LoopLinkedList":private]=>
  object(Node)#2 (3) {
    ["data"]=>
    int(1)
    ["next"]=>
    object(Node)#3 (3) {
      ["data"]=>
      int(2)
      ["next"]=>
      object(Node)#4 (3) {
        ["data"]=>
        int(3)
        ["next"]=>
        *RECURSION*
        ["previous"]=>
        *RECURSION*
      }
      ["previous"]=>
      *RECURSION*
    }
    ["previous"]=>
    object(Node)#4 (3) {
      ["data"]=>
      int(3)
      ["next"]=>
      *RECURSION*
      ["previous"]=>
      object(Node)#3 (3) {
        ["data"]=>
        int(2)
        ["next"]=>
        *RECURSION*
        ["previous"]=>
        *RECURSION*
      }
    }
  }
}

2. 查询链表中的某个节点

public function find($query) {
    $currentNode = $this->headList;
    if ($currentNode->next === $this->headList) {
        if ($currentNode->data == $query) {
            return $currentNode;
        } else {
            return NULL;
        }
    }

    $flag = false;
    while ($currentNode->next !== $this->headList) {
        if ($currentNode->data == $query) {
            $flag = true;
            return $currentNode;
        }
        $currentNode = $currentNode->next;
    }

    if ($currentNode->next === $this->headList && !$flag) {
        if ($currentNode->data == $query) {
            return $currentNode;
        }
    }
    return NULL;
}
$loop_link = new LoopLinkedList(1);
$loop_link->insert(2);
$loop_link->insert(3);
$result = $loop_link->find(2);
var_dump($result);
结果: 
object(Node)#3 (3) {
  ["data"]=>
  int(2)
  ["next"]=>
  object(Node)#4 (3) {
    ["data"]=>
    int(3)
    ["next"]=>
    object(Node)#2 (3) {
      ["data"]=>
      int(1)
      ["next"]=>
      *RECURSION*
      ["previous"]=>
      *RECURSION*
    }
    ["previous"]=>
    *RECURSION*
  }
  ["previous"]=>
  object(Node)#2 (3) {
    ["data"]=>
    int(1)
    ["next"]=>
    *RECURSION*
    ["previous"]=>
    object(Node)#4 (3) {
      ["data"]=>
      int(3)
      ["next"]=>
      *RECURSION*
      ["previous"]=>
      *RECURSION*
    }
  }
}

3. 删除链表中的指定值的节点(不过有个特殊点，该方法返回的是删除节点的下一个节点，后续实战例子将使用到)

public function display($data) {
    $currentNode = $this->headList;

    $flag = false;
    //只有一个节点的情况
    if ($currentNode->next == $this->headList) {
        if ($currentNode->data == $data) {
            $flag = true;
            $this->headList = NULL;
            return NULL;
        }
    }

    //开始节点到最后节点，不包括最后一个节点
    while ($currentNode->next !== $this->headList && !$flag) {
        if ($currentNode->data == $data) {
            $flag = true;
            $upPointer = $currentNode->previous;
            $downPointer = $currentNode->next;
            $currentNode->next->previous = $upPointer;
            $currentNode->previous->next = $downPointer;
            return $currentNode->next;
        }
        $currentNode = $currentNode->next;
    }

    //处理最后一个节点
    if ($currentNode->data = $data && !$flag) {
        $upPointer = $currentNode->previous;
        $downPointer = $currentNode->next;
        $currentNode->next->previous = $upPointer;
        $currentNode->previous->next = $downPointer;
        return $currentNode->next;
    }
}
$loop_link = new LoopLinkedList(1);
$loop_link->insert(2);
$loop_link->insert(3);
$Node = $loop_link->display(2);
var_dump($Node);
结果：
object(Node)#4 (3) {
  ["data"]=>
  int(3)
  ["next"]=>
  object(Node)#2 (3) {
    ["data"]=>
    int(1)
    ["next"]=>
    *RECURSION*
    ["previous"]=>
    *RECURSION*
  }
  ["previous"]=>
  object(Node)#2 (3) {
    ["data"]=>
    int(1)
    ["next"]=>
    *RECURSION*
    ["previous"]=>
    *RECURSION*
  }
}

至于还有别的方式，本次就不再一一介绍，接下来给大家一个实战例子

学校中经典常用到的，一群学生有各自的标号，围成一圈，一个红领巾将交给开始的学生，从这名开始学生开始计数之后每过3人，则将拿到红领巾的学生剔除，最终剩下的人一一约瑟夫环问题

约瑟夫环处理方式

//通过开始位置与偏移量，获取最后剩下的节点
public function getLastSurvivalNode($offset, $query = NULL) {
    $position = 1;

    if ($query == NULL) {
        $queryNode = $this->headList;
    } else {
        //指定位置
        $queryNode = $this->find($query);
        if ( is_null($queryNode) ) {
            echo "查询开始节点失败".PHP_EOL;
            return;
        }
    }

    while ( $queryNode->next != $queryNode ) {
        if ($position == $offset) {
            $queryNode = $this->display($queryNode->data);
            $position = 1;
        }
        $queryNode = $queryNode->next;
        $position++;
    }

    return $queryNode;
}
$loop_link = new LoopLinkedList(1);
$loop_link->insert(2);
$loop_link->insert(3);
$loop_link->insert(4);
$loop_link->insert(5);
$lastNode = $loop_link->getLastSurvivalNode(3);
var_dump($lastNode);
结果: 
object(Node)#5 (3) {
  ["data"]=>
  int(4)
  ["next"]=>
  *RECURSION*
  ["previous"]=>
  *RECURSION*
}

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author: clown