rotate-list

gistfile1.txt

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

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
 
 /*
k=2
1->2->3->4->5
.     .

1->2->3->4->5
      .     .

4->5->1->2->3

k=4;
1->2->3->4->5
.           .

2->3->4->5->1

k=5;
1->2->3->4->5
..

//if first==second then return head

k=7(same as k=2);
1->2->3->4->5
.     .

4->5->1->2>3

test cases
 {}, 0
 {1}, 1
 {1,2}, 1
 {1,2}, 2
 {1,2}, 3
 
*/
 
class Solution {
public:
    ListNode *rotateRight(ListNode *head, int k) {
        if(k <=0 || head == NULL) return head;

        ListNode* first = head;
        ListNode* second = head;
        
        //shift k nodes
        for(int i=0; i<k ; i++) {
            second = second->next;
            
            if(second == NULL) {
                k -= i;
                i = 0;
                second = head;
            }
        } 
        
        if(head == second) return head;
        
        while(second->next) {
            first = first->next;
            second = second->next;
        }
        
        second->next = head;
        head = first->next;
        first->next = NULL;
        
        return head;
    }
};