61. Rotate List

题目：

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.

链接：https://leetcode.com/problems/rotate-list/#/description

4/26/2017

19ms， 35%

先找到链表的长度，并找到相对移动的k

用快指针找到距离差，用快慢指针一起找到新的head

注意

1. 判断nodeVisited之后还有判断k在模length之后是否为0，0的话可以直接返回

2. 第19行，fast应该重新回到head

public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null) return null;
        
        int length, nodeVisited = k;
        ListNode slow = head, fast = head;

        while (fast != null && nodeVisited > 0) {
            fast = fast.next;
            nodeVisited--;
        }
        if (nodeVisited == 0 && fast == null) return head;
        else if (nodeVisited > 0) {
            length = k - nodeVisited;
            k = k % length;            
        }
        if (k == 0) return head;
        
        fast = head;
        while (k > 0) {
            fast = fast.next;
            k--;
        }

        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        ListNode temp = slow.next;
        slow.next = null;
        fast.next = head;
        return temp;

    }
}

别人的算法：

变成环，然后再来找

https://discuss.leetcode.com/topic/14470/my-clean-c-code-quite-standard-find-tail-and-reconnect-the-list

class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if(!head) return head;
        
        int len=1; // number of nodes
        ListNode *newH, *tail;
        newH=tail=head;
        
        while(tail->next)  // get the number of nodes in the list
        {
            tail = tail->next;
            len++;
        }
        tail->next = head; // circle the link

        if(k %= len) 
        {
            for(auto i=0; i<len-k; i++) tail = tail->next; // the tail node is the (len-k)-th node (1st node is head)
        }
        newH = tail->next; 
        tail->next = NULL;
        return newH;
    }
};

更多讨论：

https://discuss.leetcode.com/category/69/rotate-list