LeetCode 61 Rotate List

这道题目恶心就在于，你要判断k跟list长度之间的大小关系。

所以要先求长度。

public class Solution {
  public ListNode rotateKplace(ListNode head, int k) {
    // Write your solution here
    if (head == null || head.next == null) {
      return head;
    }
    k = k % getNum(head);
    if (k == 0) {
     return head; 
    }
    
    ListNode fast = head;
    ListNode slow = head;
    for (int i = 0; i < k - 1; i++) {
      fast = fast.next;
    }
    ListNode prev = null;
    while (fast.next != null) {
      prev = slow;
      slow = slow.next;
      fast = fast.next;
    }
    prev.next = null;
    fast.next = head;
    return slow;
  }
  
  private int getNum(ListNode head) {
    int count = 0;
    while (head != null) {
      count++;
      head = head.next; 
    }
    return count;
  }
}