61.旋转链表.cpp

/*
 * @lc app=leetcode.cn id=61 lang=cpp
 *
 * [61] 旋转链表
 */

// @lc code=start
/**
 * 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 head;
        int n = 0;
        ListNode *tail = head;
        for (auto p = head; p; p = p->next, n++) tail = p;
        k %= n; // 消除重复转圈
        if (!k) return head;
        auto p = head;
        for (int i = 0; i < n - k -1; i++) p = p->next;
        tail->next = head;
        head = p->next;
        p->next = nullptr;
        return head;
    }
};
// @lc code=end