原地反转链表

反转流程演示

并不需要真正去交换每个节点的位置，只需要更改指针的方向即可。

代码实现

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode q = head.next, p = head;
        head.next = null;
        while(q != null) {
            ListNode tmp = q.next;
            q.next = p;
            p = q;
            q = tmp;
        }
        return p;
    }
}

击败双百，bingo~