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MEDIUM

Rotate List

Given the head of a linked list, rotate the list to the right by k places.

Example

Input:

head = [1,2,3,4,5], k = 2

Output:

[4,5,1,2,3]

Explanation: Rotate the list right by 1: [5,1,2,3,4] Rotate the list right by 2: [4,5,1,2,3]

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Constraints

• The number of nodes in the list is in the range [0, 500].
• -100 ≤ Node.val ≤ 100
• 0 ≤ k ≤ 2 * 10^9

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Solution: Linked List Manipulation

• Time Complexity: O(n)
• Space Complexity: O(1)

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (!head || !head->next || k == 0) return head;
        int n = 1;
        ListNode* tail = head;
        while (tail->next) {
            tail = tail->next;
            ++n;
        }
        k = k % n;
        if (k == 0) return head;
        tail->next = head; // make it circular
        ListNode* new_tail = head;
        for (int i = 0; i < n - k - 1; ++i) {
            new_tail = new_tail->next;
        }
        ListNode* new_head = new_tail->next;
        new_tail->next = nullptr;
        return new_head;
    }
};