leetcode-rotate-list

rotate-list

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描述

Given a linked list, rotate the list to the right by k places, where k is non-negative.
Example 1:
Input: 1->2->3->4->5->NULL, k = 2
Output: 4->5->1->2->3->NULL
Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL
Example 2:
Input: 0->1->2->NULL, k = 4
Output: 2->0->1->NULL
Explanation:
rotate 1 steps to the right: 2->0->1->NULL
rotate 2 steps to the right: 1->2->0->NULL
rotate 3 steps to the right: 0->1->2->NULL
rotate 4 steps to the right: 2->0->1->NULL

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要点

将尾结点放到最前面k次

解法

class Solution {
public:
ListNode * rotateRIght(ListNode* head,int k){
if (headnull) return head;
ListNode* dummy = new ListNode(-1);
dummy->next = head;
ListNode* cur =dummy;
int length=0;
while(cur->next){
cur=cur->next;
length++;
}
if (k%length0) return head;
int cnt = length-k%length;
ListNode* back = dummy;
while(cnt–){
back=back->next;
}
dummy->next = back->next;
back->next=NULL;
cur->next = head;
return dummy->next;
}
};

struct ListNode{
int val;
ListNode* next;
ListNode(int x):val(x),next(NULL){}
};