【LeetCode】【61】【Rotate List】

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题目：Given a linked list, rotate the list to the right by k places, where k is non-negative.
解题思路：所谓链表循环右移就是头插法，但是这个题你要是一个一个得去做会导致超时，所以我们把需要移动的节点看成是一起的，以start开始，tail结束。
代码：

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) {
        val = x;
    }
}
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null)return null;
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
        ListNode pre = dummyNode;
        ListNode start = head;
        ListNode tail = head;

        int len = 1;
        while (tail.next!=null){
            len++;
            tail = tail.next;
        }
        k = k%len;
        if(k == 0)return head;
        for (int i = 0;i<len-k;i++){
            pre = pre.next;
            start = start.next;
        }
        pre.next = tail.next;
        tail.next = dummyNode.next;
        dummyNode.next = start;

        return dummyNode.next;
    }