LeetCode 61

Rotate List

Given a list, rotate the list to the right by k places,
where k is non-negative.

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

/*************************************************************************
    > File Name: LeetCode061.c
    > Author: Juntaran
    > Mail: JuntaranMail@gmail.com
    > Created Time: Tue 17 May 2016 18:47:57 PM CST
 ************************************************************************/

/*************************************************************************
    
    Rotate List
    
    Given a list, rotate the list to the right by k places, 
    where k is non-negative.

    For example:
    Given 1->2->3->4->5->NULL and k = 2,
    return 4->5->1->2->3->NULL.

 ************************************************************************/
 
#include <stdio.h>
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* rotateRight(struct ListNode* head, int k) 
{
    struct ListNode* fast = head;
    struct ListNode* slow = head;
    struct ListNode* newhead = head;
    int length = 1;
    
    if( head == NULL || k < 0 )
    {
        return head;
    }
    
    while( fast->next != NULL )
    {
        fast = fast->next;
        length ++;
    }
    fast = head;
    k = k % length;
//  printf("%d %d
",k,length);
    
    while( k > 0 )
    {
        fast = fast->next;
        if( fast == NULL )
        {
            return head;
        }
        k --;
    }
    
    while( fast->next != NULL )
    {
        slow = slow->next;
        fast = fast->next;
    }
    fast->next = head;
    newhead = slow->next;
    slow->next = NULL;
    
    return newhead;
}