61. Rotate List

题目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.

1

思路:k的值可能大于链表的长度
若0<= k <=len,则可以使用快慢指针更高效,
类似[19. Remove Nth Node From End of List])

public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null || k == 0){
            return head;
        }
       
        ListNode node = head;
        int nodeNum = 0;
        
        while(node != null){
            nodeNum++;
            node = node.next;
        }
        
        k %= nodeNum;
        if(k == 0){
            return head;
        }
       
        int secondSectionNum = nodeNum - k;
        ListNode secondTail = head;
        for(int i=1; i<secondSectionNum; i++){
            secondTail = secondTail.next;
        }
        
        ListNode firstSectionHead = secondTail.next;
        ListNode firstSectionTail = firstSectionHead;
        while(firstSectionTail.next != null){
            firstSectionTail = firstSectionTail.next;
        }
        
        secondTail.next = null;
        firstSectionTail.next = head;
        return firstSectionHead;
    }
}