61.链表旋转

Rotate List

问题描述：

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.

测试代码（python）：

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def rotateRight(self, head, k):        """        :type head: ListNode        :type k: int        :rtype: ListNode        """        if not head:            return None        if k==0:            return head        first = head        last = head        i = 0        while(i<k):            if last.next==None:                if k==i+1 or i==0:                    return head                else:                    last = head                    k = k%(i+1)                    i = 0                    continue            last = last.next            i += 1        while last.next!=None:            first = first.next            last = last.next        last.next = head        head = first.next        first.next = None        return head

性能：

参考答案：

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def rotateRight(self, head, k):        """        :type head: ListNode        :type k: int        :rtype: ListNode        """        if head is None or head.next is None or k == 0: return head        count = 0        t1 = head        t2 = head        while t1 is not None:            count += 1            t1 = t1.next        if k % count == 0: return head        for i in range(count-(k%count)-1):            t2 = t2.next        p = t2.next        t3 = p        t2.next = None        while p.next is not None:            p = p.next        p.next = head        head = t3        return head

性能：

测试代码（c++）：

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* rotateRight(ListNode* head, int k) {        if(!head)            return head;        int length = 0;        ListNode *first = head;        ListNode *last = head;        while(last)        {            last = last->next;            length++;        }        if(k==length||length==1||k%length==0)            return head;        k = k%length;        last = head;        while(last->next)        {            if(k<=0)                first = first->next;            last = last->next;            k--;        }        last->next = head;        head = first->next;        first->next =  NULL;        return head;    }};

性能：

参考答案：

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;    }};

性能：