382. Linked List Random Node

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.

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?

Example:

// Init a singly linked list [1,2,3].
ListNode head = new ListNode(1);
head.next = new ListNode(2);
head.next.next = new ListNode(3);
Solution solution = new Solution(head);

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

# @lc code=start
using LeetCode

function get_random(head::ListNode)::Int
    node, i, res = head, 1, 0
    while !isnothing(node)
        if rand(1:i) == 1  ## 1/i prob for value change
            res = node.val
        end
        node = node.next
        i += 1
    end
    return res
end
# @lc code=end

get_random (generic function with 1 method)

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