lec3_8.cpp

https://leetcode.com/problems/rotate-list/description/
/**
 * 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 == NULL || head->next==NULL)
        return head;
        //count number of nodes
        int count = 0 ;

        ListNode *temp = head;
        while(temp)
        {
            count++;
            temp = temp->next;
        }
        k = k%count;
        if(k==0) return head;
        count-=k;

        ListNode *curr = head , *prev = NULL;
        while(count--)
        {
            prev = curr;
            curr = curr->next;
        }

        prev->next = NULL;
        ListNode *Tail = curr;

        //
        while(Tail->next!=NULL)
        {
            Tail = Tail->next;
        }

        Tail->next = head;

        head = curr;
        return curr;
    }
};