day007

删除链表第n个节点

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

/*** Definition for singly-linked list.* 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; }* }*/
class Solution {public ListNode removeNthFromEnd(ListNode head, int n) {int nums=0;ListNode p=head;while(p!=null){nums++;p=p.next;}if(nums == 1)return null;if(nums == n)return head.next;n=nums-n;p=head;ListNode q=head.next;while(q!=null){n--;if(n==0){p.next=q.next;break;}p=p.next;q=q.next;}return head;}
}

图书整理1

书店店员有一张链表形式的书单，每个节点代表一本书，节点中的值表示书的编号。为更方便整理书架，店员需要将书单倒过来排列，就可以从最后一本书开始整理，逐一将书放回到书架上。请倒序返回这个书单链表。

/*** Definition for singly-linked list.* 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; }* }*/
class Solution {public int[] reverseBookList(ListNode head) {// List<Integer> list = new ArrayList<>();// ListNode q=head;// while(q != null){//     list.add(q.val);//     q=q.next;// }// int n=list.size();// int[] a =new int[n];// int j=0;// for(int i=n-1;i>=0;i--){//     a[j++]=list.get(i);// }// return a;LinkedList<Integer> stack = new LinkedList<Integer>();while(head != null) {stack.addLast(head.val);head = head.next;}int[] res = new int[stack.size()];for(int i = 0; i < res.length; i++)res[i] = stack.removeLast();return res;}
}