【无头双向链表和链表练习题2】

文章目录

以给定值x为基准将链表分割成两部分，所有小于x的结点排在大于或等于x的结点之前
输入两个链表，找出它们的第一个公共结点。
给定一个链表，判断链表中是否有环
无头双向链表的模拟实现
ArrayList（顺序表）和LinkedList（双向链表）的区别
总结

以给定值x为基准将链表分割成两部分，所有小于x的结点排在大于或等于x的结点之前

在这里插入图片描述

public class Partition {public ListNode partition(ListNode pHead, int x) {// write code here//创建四个节点ListNode bs = null;ListNode be = null;ListNode as = null;ListNode ae = null;ListNode cur = pHead; if(cur == null){return null;}while(cur != null){if(cur.val < x){//小于x放左边if(bs == null){//当bs里面没有节点时bs = cur;be = cur;     }else{//有节点了用be去遍历be.next = cur;be = cur;}}else{//大于x放右边if(as == null){//当as里面没有节点时as = cur;ae = cur;}else{//有节点了用ae去遍历ae.next = cur;ae = cur;}}cur = cur.next;}//cur遍历完了开始串起来//如果前面为空if(bs == null){return as;}//如果都不为空be.next = as;//如果后面不为空，要置为空if(as != null){ae.next = null;}return bs; 
}
}

输入两个链表，找出它们的第一个公共结点。

public class Solution {public ListNode getIntersectionNode(ListNode headA, ListNode headB){ListNode cur1 = headA;ListNode cur2 = headB; int len1 =0;int len2 = 0;//1.求链表的长度while(cur1 != null){len1++;//5cur1 = cur1.next;}while(cur2 != null){len2++;//2cur2 = cur2.next;}cur1 = headA;cur2 = headB; //int len = math.abs(len1 - len2);//3//2.走差值步if(len1>len2){for(int i = 0;i < len1-len2;i++){cur1 = cur1.next;}}else{for(int j = 0;j < len2 - len1;j++){cur2 = cur2.next;}}//3.同时走while(cur1 != cur2 ){cur1 = cur1.next;cur2 = cur2.next;}//如果没相遇，都是空if(cur1 == null){return null;}return cur1;}
}

给定一个链表，判断链表中是否有环

        public class Solution {public boolean hasCycle(ListNode head) {ListNode fast = head;ListNode slow = head;while(fast != null && fast.next != null){fast = fast.next.next;//走两步slow = slow.next;//走一步if(fast == slow){return true;}}return false;}}

无头双向链表的模拟实现

public interface IList {// 2、无头双向链表实现//头插法void addFirst(int data);void addLast(int data);//任意位置插入,第一个数据节点为0号下标void addIndex(int index,int data);//查找是否包含关键字key是否在单链表当中boolean contains(int key);//删除第一次出现关键字为key的节点void remove(int key);//删除所有值为key的节点void removeAllKey(int key);//得到单链表的长度int size();void display();void clear();
}

public class MyLinkedList implements IList {//节点内部类static class ListNode{public int val;public ListNode next;public ListNode prev;public ListNode(int val){this.val = val;}}public ListNode head;public ListNode last;@Overridepublic void addFirst(int data) {//实例化一个节点ListNode node = new ListNode(data);if (head == null){head = node;last = node;}else{node.next = head;head.prev = node;head = node;}}//尾插法@Overridepublic void addLast(int data) {ListNode node = new ListNode(data);if (last == null){last = node;head = node;}else{last.next = node;node.prev = last;last = node;}}//让cur去到index位置private ListNode findIndex(int index){ListNode cur = this.head;//index-1while(index != 0){cur = cur.next;index--;}return cur;}//   插入节点@Overridepublic void addIndex(int index, int data) {ListNode node = new ListNode(data);//检查index是否合法if(index < 0 || index >size()){//抛出自定义异常System.out.println("index不合法");return;}//头插法if(index == 0){
//            node.next = head;
//            head.prev = node;
//            head = node;addFirst(data);return;}//尾插法if (index == size()){
//            last.next = node;
//            node.prev = last;
//            last = node;addLast(data);return;}ListNode cur = findIndex(index);node.next = cur;cur.prev.next = node;node.prev = cur.prev;cur.prev = node;}@Overridepublic boolean contains(int key) {ListNode cur = head;while(cur != null){if (cur.val == key){return true;}cur = cur.next;}return false;}@Overridepublic void remove(int key) {ListNode cur = head;while (cur != null) {//如果等于关键字进入循环if (cur.val == key) {//删除头if (cur == head) {//如果只有一个节点head = head.next;//head已经删了if (head != null){//如果有很多节点head.prev = null;}last = null;} else {//删中间节点和尾巴节点的共同代码cur.prev.next = cur.next;if (cur.next == null) {//删尾巴节点last = last.prev;} else {//删中间节点cur.next.prev = cur.prev;}}return;}else{//不等于，cur往后走cur = cur.next;}}}@Overridepublic void removeAllKey(int key) {ListNode cur = head;while (cur != null) {//如果等于关键字进入循环if (cur.val == key) {//删除头if (cur == head) {//如果只有一个节点head = head.next;//head已经删了if (head != null){//如果有很多节点head.prev = null;}last = null;} else {//删中间节点和尾巴节点的共同代码cur.prev.next = cur.next;if (cur.next == null) {//删尾巴节点last = last.prev;} else {//删中间节点cur.next.prev = cur.prev;}}}//继续往后遍历cur = cur.next;}}//求链表长度@Overridepublic int size() {ListNode cur = head;int count = 0;while(cur != null){count++;cur = cur.next;}return count;}//打印链表@Overridepublic void display() {ListNode cur = head;while(cur != null){System.out.print(cur.val +" ");cur = cur.next;}System.out.println();}@Overridepublic void clear() {head = null;last = null;}
}

public class TestLink {//遍历链表public static void main(String[] args) {LinkedList<Integer> list =new LinkedList<>();list.add(1);list.add(3);list.add(5);list.add(7);list.add(9);list.add(12);System.out.println(list);System.out.println("=================");for (int i = 0; i < list.size(); i++) {System.out.print(list.get(i)+" ");}}
}