[数据结构与算法]Leetcode 61.旋转链表

/**
 * 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) {
        ListNode* pst = head;
        ListNode* last = NULL;
        int cnt = 0;
        while(pst != NULL){
            ++cnt;
            last = pst;
            pst = pst -> next;
        }
        if(cnt == 0){
            return head;
        }
        int actual = k % cnt;
        last -> next = head;
        pst = head;
        for(int i = 0; i < cnt - actual - 1 ; ++i){
            pst = pst -> next;

        } 
        head = pst -> next;
        pst->next = NULL;
        return head;
    }
};