leetcode382

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {

    ListNode head;
        Random random;
        /** @param head The linked list's head.
            Note that the head is guaranteed to be not null, so it contains at least one node. */
        public Solution(ListNode head)
        {
            this.head = head;
            random = new Random(); 
        }

        /** Returns a random node's value. */
        public int GetRandom()
        {
            ListNode c = this.head;
            int r = c.val;
            for (int i = 1; c.next != null; i++)
            {
                c = c.next;
                if (random.Next(i + 1) == i)
                {
                    r = c.val;
                }
            }

            return r;
        }
}

/**
 * Your Solution object will be instantiated and called as such:
 * Solution obj = new Solution(head);
 * int param_1 = obj.GetRandom();
 */

https://leetcode.com/problems/linked-list-random-node/#/description