编程导航算法通关村第 1关 | 链表的操作

单链表

链表的定义

/*** 单链表节点的定义*/
public class ListNode {public int val;public ListNode next;ListNode(int x) {val = x;//这个一般作用不大，写了会更加规范next = null;}
}

初始化

  public static ListNode init(ListNode head) {int i = 2;ListNode temp = head;while (i <= 10) {ListNode listNode = new ListNode(i);temp.next = listNode;temp = temp.next;i++;}return head;}

链表的遍历

/*** 遍历链表*/public static void print(ListNode head) {ListNode temp = head;while (temp != null) {System.out.println(temp.val);temp = temp.next; // 向后移动指针}}

获取链表的长度

 /*** 获取链表的长度*/public static int getLength(ListNode head) {ListNode temp = head;int length = 0;while (temp != null) {temp = temp.next; // 向后移动指针length++;}return length;}

链表的插入

• 在链表的插入中，我们需要考虑三种情况
• 头结点前插入：直接将newNode的next指向head，然后将head指向为第一个节点（newNode）

 newNode.next = head;head = newNode;return head;

• 尾结点后插入:将指针指向节点的末尾

 ListNode temp = head;
//            先将指针移动到最后while (temp.next != null) {temp = temp.next;}temp.next = newNode;return head;

• 中间插入：需要将指针指向待插入位置的前一个节点
  

//        中间插入ListNode temp = head;int i = 1;
//        将temp移动到前一个的位置,此处的位置应该是posttion-1while (i < posttion - 1) {temp = temp.next;i++;}
//        将新节点插入到temp之后newNode.next = temp.next;temp.next = newNode;return head;

• 完整代码

 /*** 插入链表 postition的范围是1——length*/public static ListNode insert(ListNode head, ListNode newNode, int posttion) {
//        分为三种情况进行讨论
//        判断参数是否合法if (head == null) {return null;}if (newNode == null) {return null;}int length = getLength(head);if (posttion <= 0 || posttion > length) {return null;}//        头部插入if (posttion == 1) {newNode.next = head;head = newNode;return head;}
//        尾部插入if (posttion == length) {ListNode temp = head;
//            先将指针移动到最后while (temp.next != null) {temp = temp.next;}temp.next = newNode;return head;}
//        中间插入ListNode temp = head;int i = 1;
//        将temp移动到前一个的位置,此处的位置应该是posttion-1while (i < posttion - 1) {temp = temp.next;i++;}
//        将新节点插入到temp之后newNode.next = temp.next;temp.next = newNode;return head;}    

链表的节点的删除

• 需要考虑三种情况
  • 节点是头节点
  • 节点是尾节点
  • 节点是中间节点

 /*** 单链表的删除*/public static ListNode delete(ListNode head, int posttion) {
//if (head == null) {return null;}if (posttion <= 0 || posttion > getLength(head)) {return null;}//        删除头结点if (posttion == 1) {head = head.next;return head;}
//    尾结点if (posttion == getLength(head)) {ListNode temp = head;while (temp.next.next != null) {temp = temp.next;}temp.next = null;
//return head;}//   删除中间节点ListNode temp = head;int i = 1;
//   移动到前一个while (i < posttion - 1) {temp = temp.next;i++;}//        删除他的下一个节点temp.next = temp.next.next;return head;}

双向链表

节点的定义

package com.lmx.project.first.bronze;class DoubleNode {public int data;    //数据域public DoubleNode next;    //指向下一个结点public DoubleNode prev;public DoubleNode(int data) {this.data = data;}//打印结点的数据域public void displayNode() {System.out.print("{" + data + "} ");}
}

双向链表的定义

• 需要定义头结点、尾结点

  private DoubleNode first; // 头结点private DoubleNode last; // 尾结点public DoublyLinkList() {first = null;last = first;}

节点的打印

  * 正序打印*/public void printOrder() {DoubleNode temp = first;while (temp != null) {temp.displayNode();temp = temp.next;}}/*** 导入打印*/public void printRevereOrder() {DoubleNode temp = last;while (temp != null) {temp.displayNode();temp = temp.prev;}}

获取长度

  /*** 获取链表长度*/public int getLength() {int length = 0;DoubleNode temp = first;while (temp != null) {length++;temp = temp.next;}return length;}

头部插入元素

 /*** 头部插入元素*/public void insertFirst(int data) {DoubleNode newNode = new DoubleNode(data);
//        没有头结点的情况if (first == null) {first = newNode;last = first;return;}newNode.next = first;first.prev = newNode;first = newNode;}

尾部插入元素

  /*** 尾插入元素*/public void insertLast(int data) {DoubleNode newNode = new DoubleNode(data);if (first == null) {first = newNode;last = first;return;}newNode.prev = last;last.next = newNode;last = newNode;}

• 中间插入元素
  

  /*** 中间插入元素*/public void insert(int data, int position) {int length = getLength();if (position <= 0 || position > length) {return;}if (position == 1) {insertFirst(data);return;}if (position == length + 1) {insertLast(data);return;}DoubleNode newNode = new DoubleNode(data);
//       中间的插入DoubleNode temp = first;int i = 1;while (i < position - 1) {temp = temp.next;i++;}
//        将结点插入到temp后面temp.next.prev = newNode;newNode.next = temp.next;temp.next = newNode;newNode.prev = temp;}

链表的删除

/*** 链表的删除*/public DoubleNode delete(int key) {
//DoubleNode temp = first;while (temp != null && temp.data != key) {temp = temp.next;}if (temp == null) {return temp;}
//        如果是头结点if (temp == first) {first = first.next;first.prev = null;} else if (temp == last) {//        如果是尾结点last.prev.next = null;} else {//        如果是中间节点temp.next.prev = temp.prev;temp.prev.next = temp.next;temp.next = null;temp.prev = null;}return temp;}