[LeetCode] 382. Linked List Random Node

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

    List<ListNode> array = new ArrayList<>();
    /** @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) {
        ListNode p = head;
        while (p != null) {
            array.add(p);
            p = p.next;
        }
    }
    
    /** Returns a random node‘s value. */
    public int getRandom() {
        Random random = new Random();
        int index = random.nextInt(array.size());
        return array.get(index).val;
    }
}

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