Rotate List

• Time : $O(B)$
• Space : $O(B)$

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
ListNode* Solution::rotateRight(ListNode* A, int B) {
    ListNode* runner = A;
    for(int i = 0; i < B; i++) {
        runner = runner->next;
        if(!runner) runner = A;
    }
    if(runner == A) return A;
    ListNode* head = A;
    while(runner->next) {
        runner = runner->next;
        head = head->next;
    }
    runner->next = A;
    ListNode* res = head->next;
    head->next = NULL;
    return res;
}