数组，链表

ArrayList<String> list = new ArrayList<String>();
list.add(E element);
list.get(int index)
list.indexOf(Object o)
list.remove(int index)
list.size()

数组：
int [] a = new int[5]
//全部初始化为-1
Arrays.fill(m, -1);
a.length

str.length()

public static ListNode rotateRight(ListNode head, int n) {
        if(head == null || head.next == null || n == 0)
            return head;
        ListNode fast = head, slow = head, countlen = head;
        ListNode newhead = new ListNode(-1);
        int len = 0;
        //先获得链表长度
        while(countlen != null){
            len++;
            countlen = countlen.next;
        }
        //n是可以大于整个链表长度的，所以这个时候取余即可
        //如果余数为0，相当于没有旋转
        n = n % len;
        if(n == 0)
            return head;
        
        //先移动快指针走k步
        for(int i = 0; i < n; i++)
            fast = fast.next;
        
        //然后两个指针一起走，直到快指针走到末尾
        while(fast.next != null){
            slow = slow.next;
            fast = fast.next;
        }
        
        //这个时候慢指针的下一个位置就是旋转之后的链表的第一个结点
        newhead = slow.next;
        fast.next = head;
        slow.next = null;
        
        return newhead;
    }