java实现---查找单链表的倒数第K个节点，要求只能遍历一次链表；；；删除链表的倒数第k个节点

查找单链表的倒数第K个节点，要求只能遍历一次链表

• 定义两个前后节点forward和backward
• 先让forward走 k 步，再让forward和backward一起走，当forward走到空，此时backward就走到了倒数第k步

class ListNode{
    int data;
    ListNode next;
}
public class Link{
    public static void FindTailK(ListNode first,int k){
        ListNode forward = first;
        ListNode backward = first;
        while(k-- != 0){
            forward = forward.next;
        }
        while(forward != null){
            forward = forward.next;
            backward = backward.next;
        }
        System.out.println(backward.data);
    }
    public static void main(String[] args) {
        ListNode n1 = new ListNode();
        ListNode n2 = new ListNode();
        ListNode n3 = new ListNode();
        ListNode n4 = new ListNode();
        ListNode n5 = new ListNode();
        n1.data = 1;
        n2.data = 2;
        n3.data = 3;
        n4.data = 4;
        n5.data = 5;
        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
        n4.next = n5;
        FindTailK(n1,2);
    }
}

删除链表的倒数第k个节点

• 想要删除倒数第k个节点，可以找到倒数第k+1个节点，即k的前一个节点
• 第二步让k的前一个节点的next指向k的后一个节点
• 即k节点就相当于被删除啦

public class Link{
    public static ListNode DeleteTailK(ListNode first,int k){
        ListNode forward = first;
        ListNode backward = first;
        while(k-- != 0){
            forward = forward.next;
        }
        while(forward.next != null){   //即最后的backward为k的前一个节点
            forward = forward.next;
            backward = backward.next;
        }
        backward.next = backward.next.next;
        return first;

    }
        public static void print(ListNode head){
        while(head != null){
            System.out.println(head.data);
            head = head.next;
        }
   }