382 - Linked List Random Node.

Medium

Given a singly linked list, return a random node's value from the linked list. Each node must have the same probability of being chosen.

Implement the Solution class:

• Solution(ListNode head) Initializes the object with the integer array nums.

• int getRandom() Chooses a node randomly from the list and returns its value. All the nodes of the list should be equally likely to be choosen.

Example 1:

Input

["Solution", "getRandom", "getRandom", "getRandom", "getRandom", "getRandom"]
[[[1, 2, 3]], [], [], [], [], []]

Output:

[null, 1, 3, 2, 2, 3]

Explanation:

Solution solution = new Solution([1, 2, 3]);
solution.getRandom(); // return 1
solution.getRandom(); // return 3
solution.getRandom(); // return 2
solution.getRandom(); // return 2
solution.getRandom(); // return 3
// getRandom() should return either 1, 2, or 3 randomly. Each element should have equal probability of returning.

Constraints:

• The number of nodes in the linked list will be in the range <code>1, 10⁴</code>.

• <code>-10⁴<= Node.val <= 10⁴</code>

• At most <code>10⁴</code> calls will be made to getRandom.

Follow up:

• What if the linked list is extremely large and its length is unknown to you?

• Could you solve this efficiently without using extra space?