382. Linked List Random Node

     /*
      * 382. Linked List Random Node
      * 2016-8-20 by Mingyang
      * 直接进行长度计算就好了，再根据随机数，便利到指定的位置找到结果
      */
     class Solution {
            int len = 0;
            ListNode head;
            /** @param head The linked list‘s head. Note that the head is guanranteed to be not null, so it contains at least one node. */
            public Solution(ListNode head) {
                this.head = head;
                ListNode cur = head;
                while(cur!=null){
                    len++;
                    cur = cur.next;
                }
            }
            
            /** Returns a random node‘s value. */
            public int getRandom() {
                int r = (int)(Math.random() * len);
                ListNode cur = head;
                while(r > 0){
                    cur = cur.next;
                    r--;
                }
                return cur.val;
            }
        }