链表是由一组节点组成的集合。每个节点都使用一个对象的引用指向它的后继。指向另一个节点的引用叫做链表。
插入:链表中插入一个节点的效率很高。向链表中插入一个节点,需要修改它前面的节点(前驱),使其指向新加入的节点,而新加入的节点则指向原来前驱指向的节点(见下图)。
由上图可知,B、C之间插入D,三者之间的关系为
current为插入节点的前驱节点 current->next = new // B节点指向新节点D new->next = current->next // 新节点D指向B的后继节点C
删除:从链表中删除一个元素,将待删除元素的前驱节点指向待删除元素的后继节点,同时将待删除元素指向 null,元素就删除成功了(见下图)。
由上图可知,A、C之间删除B,三者之间的关系为
current为要删除节点的前驱节点 current->next = current->next->next // A节点指向C节点
具体代码如下:
1 <?php 2 // 节点类 3 class Node { 4 public $data; // 节点数据 5 public $next; // 下一节点 6 7 public function __construct($data) { 8 $this->data = $data; 9 $this->next = NULL; 10 } 11 } 12 // 单链表类 13 class SingleLinkedList { 14 private $header; // 头节点 15 16 function __construct($data) { 17 $this->header = new Node($data); 18 } 19 // 查找节点 20 public function find($item) { 21 $current = $this->header; 22 while ($current->data != $item) { 23 $current = $current->next; 24 } 25 return $current; 26 } 27 // (在节点后)插入新节点 28 public function insert($item, $new) { 29 $newNode = new Node($new); 30 $current = $this->find($item); 31 $newNode->next = $current->next; 32 $current->next = $newNode; 33 return true; 34 } 35 36 // 更新节点 37 public function update($old, $new) { 38 $current = $this->header; 39 if ($current->next == null) { 40 echo "链表为空!"; 41 return; 42 } 43 while ($current->next != null) { 44 if ($current->data == $old) { 45 break; 46 } 47 $current = $current->next; 48 } 49 return $current->data = $new; 50 } 51 52 // 查找待删除节点的前一个节点 53 public function findPrevious($item) { 54 $current = $this->header; 55 while ($current->next != null && $current->next->data != $item) { 56 $current = $current->next; 57 } 58 return $current; 59 } 60 61 // 从链表中删除一个节点 62 public function delete($item) { 63 $previous = $this->findPrevious($item); 64 if ($previous->next != null) { 65 $previous->next = $previous->next->next; 66 } 67 } 68 69 // findPrevious和delete的整合 70 public function remove($item) { 71 $current = $this->header; 72 while ($current->next != null && $current->next->data != $item) { 73 $current = $current->next; 74 } 75 if ($current->next != null) { 76 $current->next = $current->next->next; 77 } 78 } 79 80 // 清空链表 81 public function clear() { 82 $this->header = null; 83 } 84 85 // 显示链表中的元素 86 public function display() { 87 $current = $this->header; 88 if ($current->next == null) { 89 echo "链表为空!"; 90 return; 91 } 92 while ($current->next != null) { 93 echo $current->next->data . "  "; 94 $current = $current->next; 95 } 96 } 97 } 98 99 $linkedList = new SingleLinkedList('header'); 100 $linkedList->insert('header', 'China'); 101 $linkedList->insert('China', 'USA'); 102 $linkedList->insert('USA','England'); 103 $linkedList->insert('England','Australia'); 104 echo '链表为:'; 105 $linkedList->display(); 106 echo "</br>"; 107 echo '-----删除节点USA-----'; 108 echo "</br>"; 109 $linkedList->delete('USA'); 110 echo '链表为:'; 111 $linkedList->display(); 112 echo "</br>"; 113 echo '-----更新节点England为Japan-----'; 114 echo "</br>"; 115 $linkedList->update('England', 'Japan'); 116 echo '链表为:'; 117 $linkedList->display(); 118 //echo "</br>"; 119 //echo "-----清空链表-----"; 120 //echo "</br>"; 121 //$linkedList->clear(); 122 //$linkedList->display(); 123 124 // 输出: 125 链表为:China USA England Australia 126 -----删除节点USA----- 127 链表为:China England Australia 128 -----更新节点England为Japan----- 129 链表为:China Japan Australia 130 131 PHP实现单链表
二、双链表
current为插入节点的前驱节点 current->next = new // B的next属性指向新节点D new->next = current->next // 新节点D的next属性指向B的后继节点C current->next->previous = new // B的后继节点C的previous属性指向新节点D(原先是C的previous属性指向B)
current为要删除的节点 current->previous->next = current->next // B的前驱节点A的next属性指向B的后继节点C current->next->previous = current->previous // B的后继节点C的previous属性指向B的前驱节点A current->previous = null // B的previous属性指向null current->next = null // B的next属性指向null
1 <?php 2 // 节点类 3 class Node { 4 public $data; // 节点数据 5 public $previous = NULL; // 前驱 6 public $next = NULL; // 后继 7 8 public function __construct($data) { 9 $this->data = $data; 10 $this->previous = NULL; 11 $this->next = NULL; 12 } 13 } 14 // 双链表类 15 class DoubleLinkedList { 16 private $header; // 头节点 17 18 function __construct($data) { 19 $this->header = new Node($data); 20 } 21 // 查找节点 22 public function find($item) { 23 $current = $this->header; 24 while ($current->data != $item) { 25 $current = $current->next; 26 } 27 return $current; 28 } 29 // 查找链表最后一个节点 30 public function findLast() { 31 $current = $this->header; 32 while ($current->next != null) { 33 $current = $current->next; 34 } 35 return $current; 36 } 37 //(在节点后)插入新节点 38 public function insert($item, $new) { 39 $newNode = new Node($new); 40 $current = $this->find($item); 41 $newNode->next = $current->next; 42 $newNode->previous = $current; 43 $current->next = $newNode; 44 return true; 45 } 46 // 从链表中删除一个节点 47 public function delete($item) { 48 $current = $this->find($item); 49 if ($current->next != null) { 50 $current->previous->next = $current->next; 51 $current->next->previous = $current->previous; 52 $current->next = null; 53 $current->previous = null; 54 return true; 55 } 56 } 57 // 显示链表中的元素 58 public function display() { 59 $current = $this->header; 60 if ($current->next == null) { 61 echo "链表为空!"; 62 return; 63 } 64 while ($current->next != null) { 65 echo $current->next->data . "  "; 66 $current = $current->next; 67 } 68 } 69 // 反序显示双向链表中的元素 70 public function dispReverse() { 71 $current = $this->findLast(); 72 while ($current->previous != null) { 73 echo $current->data . "  "; 74 $current = $current->previous; 75 } 76 } 77 } 78 79 // 测试 80 $linkedList = new DoubleLinkedList('header'); 81 $linkedList->insert('header', 'China'); 82 $linkedList->insert('China', 'USA'); 83 $linkedList->insert('USA','England'); 84 $linkedList->insert('England','Australia'); 85 echo '链表为:'; 86 $linkedList->display(); 87 echo "</br>"; 88 echo '-----删除节点USA-----'; 89 echo "</br>"; 90 $linkedList->delete('USA'); 91 echo '链表为:'; 92 $linkedList->display(); 93 94 // 输出: 95 链表为:China USA England Australia 96 -----删除节点USA----- 97 链表为:China England Australia 98 99 PHP实现双链表
三、循环链表
current为插入节点的前驱节点 // 中间 current->next = new // B节点指向新节点D new->next = current->next // 新节点D指向B的后继节点C // 尾端 current->next = new // C节点指向新节点D new->next = header // 新节点D指向头节点Header
current为要删除节点的前驱节点 // 中间 current->next = current->next->next // A节点指向C节点 // 尾端 current->next = header // B节点指向头节点Header
1 <?php 2 // 节点类 3 class Node { 4 public $data; // 节点数据 5 public $previous; 6 public $next; // 下一节点 7 8 public function __construct($data) { 9 $this->data = $data; 10 $this->next = NULL; 11 } 12 } 13 // 循环链表类 14 class CircularLinkedList { 15 private $header; // 头节点 16 17 function __construct($data) { 18 $this->header = new Node($data); 19 $this->header->next = $this->header; 20 } 21 // 查找节点 22 public function find($item) { 23 $current = $this->header; 24 while ($current->data != $item) { 25 $current = $current->next; 26 } 27 return $current; 28 } 29 // 插入新节点 30 public function insert($item, $new) { 31 $newNode = new Node($new); 32 $current = $this->find($item); 33 if ($current->next != $this->header) { // 链表中间 34 $current->next = $newNode; 35 $newNode->next = $current->next; 36 } else { // 链表尾端 37 $current->next = $newNode; 38 $newNode->next = $this->header; 39 } 40 return true; 41 } 42 // 删除节点 43 public function delete($item) { 44 $current = $this->header; 45 while ($current->next != null && $current->next->data != $item) { 46 $current = $current->next; 47 } 48 if ($current->next != $this->header) { // 链表中间 49 $current->next = $current->next->next; 50 } else { // 链表尾端 51 $current->next = $this->header; 52 } 53 } 54 // 显示链表中的元素 55 public function display() { 56 $current = $this->header; 57 while ($current->next != $this->header) { 58 echo $current->next->data . "  "; 59 $current = $current->next; 60 } 61 } 62 } 63 64 // 测试 65 $linkedList = new CircularLinkedList('header'); 66 $linkedList->insert('header', 'China'); 67 $linkedList->insert('China', 'USA'); 68 $linkedList->insert('USA', 'England'); 69 $linkedList->insert('England', 'Australia'); 70 echo '链表为:'; 71 $linkedList->display(); 72 echo "</br>"; 73 echo '-----删除节点USA-----'; 74 echo "</br>"; 75 $linkedList->delete('USA'); 76 echo '链表为:'; 77 $linkedList->display(); 78 // 输出: 79 链表为:China USA England Australia 80 -----删除节点USA----- 81 链表为:China England Australia 82 83 PHP实现循环链表