61. Rotate List

https://leetcode.com/problems/rotate-list/

Rotate List - LeetCode

/**
 * 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 || head->next == nullptr) return head;
        
        ListNode* end = head;
        ListNode* newTail = head;
        ListNode* newHead;
        int cnt = 1;
        while(end->next) {
            end = end->next;
            cnt++;
        }
        k = k % cnt;
        while(cnt - k - 1 != 0) {
            newTail = newTail->next;
            cnt--;
        }  
        
        end->next = head;
        newHead = newTail->next;
        newTail->next = nullptr;
        
        return newHead;
    }
};

아래 것은 처음 것. test만 통과하고 wrong answer.

/**
 * 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* end = head;
        ListNode* tempNext = head;
        ListNode* tempPrev = head;
        int cnt = -1;
        while(end->next) {
            end = end->next;
            cnt++;
        }
        while(cnt != 0) {
            tempPrev = tempNext;
            tempNext = tempPrev->next;
            cnt--;
        }  
        tempPrev->next = nullptr;
        end->next = head;
        head = tempNext;
        return head;
    }
};