链表经典算法题实现

本文包含链表的以下内容：

　　1、单链表的创建和遍历

　　2、求单链表中节点的个数

　　3、查找单链表中的倒数第k个结点（剑指offer，题15）

　　4、查找单链表中的中间结点

　　5、合并两个有序的单链表，合并之后的链表依然有序【出现频率高】（剑指offer，题17）

　　6、单链表的反转【出现频率最高】（剑指offer，题16）

　　7、从尾到头打印单链表（剑指offer，题5）

　　8、判断单链表是否有环

　　9、取出有环链表中，环的长度

　　10、单链表中，取出环的起始点（剑指offer，题56）。本题需利用上面的第8题和第9题。

　　11、判断两个单链表相交的第一个交点（剑指offer，题37）

package com.he;import java.util.Stack;import com.he.LinkList.Node;public class test32 {class Node{int data;Node next;Node(int data){this.data = data;}}public Node head =null;    public Node current = null;    //添加节点    public void add(int data){    if(head==null){    head = new Node(data);    current = head;    }else{    current.next = new Node(data);    current = current.next;    }    }    //方法重载：向链表中添加结点    public void add(Node node){    if(head==null){    head = node;    current = node;    }else{    current.next = node;    current = current.next;    }    }        //遍历节点    public void print(Node node){        current = node;        while(current!=null){        System.out.println(current.data);        current = current.next;        }    }    //求单链表节点    public int getLength(Node node){    current = node;    int length = 0;    if(current == null){    return 0;    }    while(current!=null){    length++;    current = current.next;       }return length;          }    //查找单链表中的倒数第k个结点    public Node findLastNode(Node node,int k){    if(node==null || k==0){    return null;    }    Node first = node;    Node second = node;    for (int i = 0; i < k-1; i++) {second = second.next;if(second == null){return null;}}    while(second.next!=null){    first = first.next;    second = second.next;    }    return first;    }        //查找单链表中的中间结点    public Node findMiddle(Node node){    if(node==null){    return null;    }    Node first = node;    Node second = node;    while(first!=null && second!=null){    if(second.next!=null){    second = second.next.next;    }else{    return first;    }       first = first.next;    }    return first;    }       //合并两个有序的单链表，合并之后的链表依然有序    public Node getMergeLinkList(Node head1,Node head2){    if(head1==null && head2==null){    return null;    }    if(head1==null){    return head2;    }    if(head2==null){    return head1;    }    Node head;    Node current;    if(head1.data < head2.data){    head = head1;    current = head1;    head1 = head1.next;    }else{    head = head2;    current = head2;    head2 = head2.next;    }    while(head1!= null && head2!= null){    if(head1.data < head2.data){    current.next = head1;    current = current.next;    head1 = head1.next;    }else{    current.next = head2;    current = current.next;    head2 = head2.next;    }    }    if(head1 == null){    current.next = head2;    }    if(head2 == null){    current.next = head1;    }    return head;    }    //单链表的反转    public Node reverseList(Node head){    if(head==null && head.next==null){    return head;    }    Node reverseHead = null;    Node next = null;    Node current = head;    while(current!=null){    next = current.next;    current.next = reverseHead;    reverseHead = current;    current = next;    }    return reverseHead;    }        //从尾到头打印单链表    public void reversePrint(Node head){    if(head == null){    return;    }    Stack<Node> stack = new Stack<Node>();    Node current = head;    while(current!=null){    stack.push(current);    current = current.next;    }    while(stack.size()>0){    System.out.println(stack.pop().data);    }    }        //判断单链表是否有环    public boolean hasCycle(Node head){    if(head == null){    return false;    }    Node first = head;    Node second = head;    while(second!=null){    first = first.next;    if(second.next!=null){    second = second.next.next;    }else{    return false;    }        if(first == second){    return true;    }    }    return false;    }       //取出有环链表中，环的长度    public int getCycleLength(Node node){    int length = 0;    Node current = node;    while(current!=null){    current = current.next;    length++;    if(current == node){    return length;    }    }    return length;    }        //单链表中，取出环的起始点    public Node getCycleStart(Node head,int cycleLength){    if(head==null){    return null;    }    Node first = head;    Node second = head;    for (int i = 0; i < cycleLength; i++) {second = second.next;}    while(first!=null&& second!=null){    if(first == second){    return first;    }    first = first.next;    second = second.next;    }    return null;    }        //求两个单链表相交的第一个交点    public Node getFirstCommonNode(Node head1,Node head2){    if(head1==null|| head2==null){    return null;    }    int length1 = getLength(head1);    int length2 = getLength(head2);    int lengthDif = 0;    Node longHead = null;    if(length1 > length2){    lengthDif = length1-length2;    longHead = head1;    }else{    lengthDif = length2-length1;    longHead = head2;    }    for (int i = 0; i < lengthDif; i++) {    longHead = longHead.next;}    while(longHead!=null && head2!=null){    longHead = longHead.next;    head2 = head2.next;    if(longHead == head2){    return head2;    }    }return null;        }        public static void main(String[] args) {    test32 sh = new test32();    for (int i = 0; i < 4; i++) {sh.add(i);}   // sh.print(sh.head);   // System.out.println(sh.getLength(sh.head));   // System.out.println(sh.findLastNode(sh.head, 3).data);   //sh.print(sh.reverseList(sh.head));    sh.add(sh.head);    System.out.println(sh.hasCycle(sh.head));    System.out.println(sh.hasCycle(sh.head));    System.out.println(sh.getCycleLength(sh.head));    System.out.println(sh.getCycleStart(sh.head, sh.getCycleLength(sh.head)).data);      //    test32 sh1 = new test32();//    for (int i = 6; i < 8; i++) {//sh1.add(i);//} //    sh.print(sh.getMergeLinkList(sh.head, sh1.head));    }}