最强单链表合集（二）相关题解

一、计算链表中节点个数

  /**
    * @param head  不计算头结点
    * @return count 链表中的结点个数
    */
 public static int getLength(Node head) {
    
    
  if(head.next==null) {
    
    
      return 0;
  }
  Node temp =head.next;
  int count=0;
  while(temp!=null){
    
    
      count++;
      temp=temp.next;
  }
  return count;
 }

二、查找倒数第k个节点

    /**
     * @param k
     * @param head
     * @return 返回倒数第k个节点
     */
 public static Node findIndexNode(int k,Node head){
    
    
      if(head.next == null){
    
    
          System.out.println("链表为空");
          return:
      }
      int size = getLength(head);
      int num = size-k; //要遍历的次数
      Node temp = head.next;
     for(int i =0;i<num;i++){
    
    
         temp=temp.next;
     }
     return temp;
 }

三、单链表的反转

public static void reverse(Node head) {
    
    
     if(head.next ==null||head.next.next==null){
    
    
         return;
     }
     Node cur=head.next;
     Node next=null;
     Node newList=new Node(0);
     while(cur!=null){
    
    
         next=cur.next; //next保存下一节点
         cur.next =newList.next; //将cur的下一节点加入新链表的最前端
         newList.next=cur; //当前节点链接到新链表
         cur=next; //cur指向下一节点
     }
     head.next=newList.next;
}

四、从尾到头打印单链表

 public static void reversePrint(Node head) {
    
    
        Stack<Node> stack = new Stack();
        Node temp = head.next;
        //将所有节点压入栈
        while (temp != null) {
    
    
            stack.push(temp);
            temp = temp.next;
        }
        //当栈不为空时，弹栈并显示
        while (!stack.isEmpty()){
    
    
            System.out.println(stack.pop());
        }
    }

五、删除排序链表中的重复元素（不带头结点）

 * public class ListNode {
    
    
 *     int val;
 *     ListNode next;
 *     ListNode() {
    
    }
 *     ListNode(int val) {
    
     this.val = val; }
 *     ListNode(int val, ListNode next) {
    
     this.val = val; this.next = next; }
 * }
public ListNode deleteDuplicates(ListNode head) {
    
    
    if(head == null){
    
    
        return null;
    }
    ListNode node = head;
    while(node!=null&&node.next!=null){
    
    
        if(node.val==node.next.val){
    
    
            node.next= node.next.next;
        }
        else{
    
    
            node=node.next;
        }
    }
    return head;
    }

六、判断链表是否有环（不带头结点）

快指针比慢指针每次走两步

 * public class ListNode {
    
    
 *     int val;
 *     ListNode next;
 *     ListNode() {
    
    }
 *     ListNode(int val) {
    
     this.val = val; }
 *     ListNode(int val, ListNode next) {
    
     this.val = val; this.next = next; }
 * }
   public boolean hasCycle(ListNode head) {
    
    
    if (head == null || head.next == null) {
    
    
        return false;
    }
    ListNode slow = head;
    ListNode fast = head.next;
    while (slow != fast) {
    
    
        if (fast == null || fast.next == null) {
    
    
            return false;
        }
        slow = slow.next;
        fast = fast.next.next;
    }
    return true;
}    

七、返回环形链表中的第一个结点（不带头结点）

 * public class ListNode {
    
    
 *     int val;
 *     ListNode next;
 *     ListNode() {
    
    }
 *     ListNode(int val) {
    
     this.val = val; }
 *     ListNode(int val, ListNode next) {
    
     this.val = val; this.next = next; }
 * }
    public ListNode detectCycle(ListNode head) {
    
    
        if( head == null || head.next ==null){
    
    
            return null;
        }
        ListNode slow =head;
        ListNode fast= head;
        while(fast!=null){
    
    
          slow = slow.next;
          if(fast.next != null){
    
    
              fast=fast.next.next;
          }else{
    
    
              return null;
          }
          if(fast == slow){
    
    
              ListNode temp = head;
              while(temp!=slow){
    
    
                  temp=temp.next;
                  slow=slow.next;
              }
              return temp;
          }
        }
        return null;

八、两两交换链表中的结点（不带头结点）

 * public class ListNode {
    
    
 *     int val;
 *     ListNode next;
 *     ListNode() {
    
    }
 *     ListNode(int val) {
    
     this.val = val; }
 *     ListNode(int val, ListNode next) {
    
     this.val = val; this.next = next; }
 * }
 public ListNode swapPairs(ListNode head) {
    
    
        ListNode pre =new ListNode(0);
        pre.next =head;
        ListNode temp = pre;
        while(temp.next!=null&&temp.next.next!=null){
    
    
            ListNode node1 = temp.next;
            ListNode node2=temp.next.next;  
            temp.next= node2;              //交换前后结点
            node1.next =node2.next;
            node2.next =node1;
            temp=node1;
        }
        return pre.next;
    }