Leetcode第92题 反转链表_leetcode 92

1. 算法
   头插法、双指针
2. 核心思想
   一般对于链表问题，都要考虑在链表头上加一个0结点，方便进行下一步处理。头插法即为在头指针后面添加结点。设置两个结点，一个结点保持在right-1的位置，另外一个结点从right开始，一步步往下移动，直到left。
3. 代码

/**
 * 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 reverseBetween(ListNode head, int left, int right) {
        ListNode firstHead = new ListNode(0,head);
        ListNode secondHead = new ListNode(0,head);
        ListNode result = firstHead;
        int len = 0;
        while(len != left - 1){
            firstHead = firstHead.next;
            secondHead = secondHead.next;
            len++;
        }
        secondHead = secondHead.next;

        for(int i = 0;i < right - left;i++){
            ListNode temp = secondHead.next;
            secondHead.next = temp.next;
            temp.next = firstHead.next;
            firstHead.next = temp;
        }

        return result.next;

    }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34