92

92. Reverse Linked List II (Medium)

Given the head of a singly linked list and two integers left and right where left <= right, reverse the nodes of the list from position left to position right, and return the reversed list.

 

Example 1:

Input: head = [1,2,3,4,5], left = 2, right = 4
Output: [1,4,3,2,5]

Example 2:

Input: head = [5], left = 1, right = 1
Output: [5]

 

Constraints:

• The number of nodes in the list is n.
• 1 <= n <= 500
• -500 <= Node.val <= 500
• 1 <= left <= right <= n

 

Follow up: Could you do it in one pass?

Companies:
Microsoft, Amazon, Facebook, Bloomberg

Related Topics:
Linked List

Similar Questions:

• Reverse Linked List (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/reverse-linked-list-ii/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        ListNode dummy, *p = &dummy;
        dummy.next = head;
        for (int i = 1; i < m; ++i) p = p->next;
        auto q = p->next, tail = q;
        for (int i = m; i <= n; ++i) {
            auto node = q;
            q = q->next;
            node->next = p->next;
            p->next = node;
        }
        tail->next = q;
        return dummy.next;
    }
};