Q20 LeetCode19 删除链表倒数第N个节点

1.创建虚拟头结点ListNode pre=new ListNode(0,head);

2.创建快慢节点

3.快节点fastIndex先往后移N个位置

4.快慢slowIndex节点一直往后移，直至快节点到链表末尾

5.删除慢节点后面的节点

 

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode pre=new ListNode(0,head);
        ListNode fastIndex=pre;
        ListNode slowIndex=pre;
        for(int i=0;i<n;i++){
            fastIndex=fastIndex.next;
        }
        while(fastIndex.next!=null){
            fastIndex=fastIndex.next;
            slowIndex=slowIndex.next;
        }
        if(slowIndex.next!=null){
            slowIndex.next=slowIndex.next.next;
        }
        return pre.next;

    }
}