LeetCode --- 92. Reverse Linked List II

92. Reverse Linked List II

Difficulty: Medium

Reverse a linked list from position m to n. Do it in one-pass.

**Note: **1 ≤ m ≤ n ≤ length of list.

Example:

Input: 1->2->3->4->5->NULL, m = 2, n = 4
Output: 1->4->3->2->5->NULL

Solution

思路

这个有点难懂，画个图看看。。。

Language: C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        if (!head)  return head;
        ListNode* newHead = new ListNode(0), *pre = newHead, *cur;
        newHead->next = head;
        for (int i = 1; i < m; i++)
            pre = pre->next;
        cur = pre->next;
        for (int i = 0; i < n - m; i++){
            ListNode* temp = cur->next;
            cur->next = temp->next;
            temp->next = pre->next;
            pre->next = temp;
        }
        return newHead->next;
    }
};