Linked List Random Node Python Solution

lcpy gen -n 382   # by problem number
lcpy gen -s linked_list_random_node   # by problem name

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.

Input
["Solution", "getRandom", "getRandom"]
[[[7]], [], []]
Output
[null, 7, 7]

Explanation
Solution solution = new Solution([7]);
solution.getRandom(); // return 7, the only node in the list.

import random

from leetcode_py import ListNode


class Solution:
    # Time: init O(1), get_random O(n)
    # Space: O(1)
    def __init__(self, head: ListNode[int] | None) -> None:
        self.head = head

    def get_random(self) -> int:
        node = self.head
        assert node is not None
        reservoir = node.val
        current = node.next
        seen = 2
        while current is not None:
            if random.randint(1, seen) == 1:
                reservoir = current.val
            current = current.next
            seen += 1
        return reservoir