c_cpp 61.轮换名单 - 中 - 2018.8.10

Posted 2021-05-14

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (head == NULL) return NULL;
        int nodeNum = 1;
        ListNode *tailNode = head;
        // 找尾节点
        while (tailNode->next != NULL) {
            nodeNum += 1;
            tailNode = tailNode->next;
        }
        k = k % nodeNum;
        if (k <= 0) {
            return head;
        }
        // 新的头节点的 index
        k = nodeNum - k;
        ListNode *newHead = head;
        ListNode *preNode;
        while (k > 0) {
            preNode = newHead;
            newHead = newHead->next;
            k--;
        }
        preNode->next = NULL;
        tailNode->next = head;
        return newHead;
    }
};