Leetcode：206. Reverse Linked List

public class Solution {   public ListNode reverseList(ListNode head) {        if(head != null) {            ListNode p = head; //指向当前元素            ListNode frontier; //p的下一个元素，每次循环都会反转到head处            while(p != null && p.next != null) {                frontier = p.next;                p.next = p.next.next;                frontier.next = head;                head = frontier;            }