0382. Linked List Random Node

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

Description

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 [1, 104].

• -104 <= Node.val <= 104

• At most 104 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?

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