Description

Submission

/**
 * 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 == nullptr) return nullptr;
        if(k == 0) return head;
        int len = 0;
        ListNode *res, *endPtr;
        for(ListNode* ptr = head; ptr != nullptr; ptr = ptr->next, len++){
            endPtr = ptr;
        }
        k = k % len;
        if(k == 0) return head;
        ListNode* ptr = head;
        for(int i = 0; i < len - k - 1; ++i, ptr = ptr->next);
        res = ptr->next;
        ptr->next = nullptr;
        endPtr->next = head;
        return res;
    }
};

Submission 210327

/**
 * 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) return nullptr;
        
        int cnt = 0;
        ListNode* tail = head;
        for(; tail->next; tail = tail->next, cnt++);
        cnt++;
        k %= cnt;
        if(k == 0 || !head->next) return head;

        ListNode* node = head;
        for(int i = 0; i < cnt - k - 1; ++i, node = node->next);

        ListNode* ret = node->next;
        node->next = nullptr;
        tail->next = head;

        return ret;
    }
};