61.鏈表旋轉

Rotate List

問題描述：

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.

測試代碼（python）：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class 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：

參考答案：

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class 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：

測試代碼（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：

參考答案：

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：