Rotate List

Given a list, rotate the list to the right by k places, where k is non-negative.

Example

Given 1->2->3->4->5 and k = 2, return 4->5->1->2->3.

分析：

先得到list size, 然后 k = k % size. 找到新head，然后把tail链接到head.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param head: the List
     * @param k: rotate to the right k places
     * @return: the list after rotation
     */
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null || head.next == null) return head; 
        // write your code here
        int size = size(head);
        k = k % size;
        
        if (k == 0) return head;
        ListNode pointer = head;
        for (int i = 1; i <= size - k - 1; i++) {
            pointer = pointer.next;
        }
        
        ListNode newHead = pointer.next;
        pointer.next = null;
        
        // link the tail to the head
        ListNode current = newHead;
        while (current.next != null) {
            current = current.next;
        }
        current.next = head;
        return newHead;
    }
    
    public int size(ListNode head) {
        int count = 0;
        while (head != null) {
            count++;
            head = head.next;
        }
        return count;
    }
}

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