Practice Linked List Random Node

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#382

LeetCode Problem

Linked List Random Node

Linked List Math Reservoir Sampling Randomized

Problem Statement

Solution(head) receives a nonempty singly linked list. getRandom() returns a node value, selecting each node with equal probability. Equal values in different nodes remain distinct sampling opportunities. Practice approach: Reservoir sampling uses O(1) extra space without needing the list length. During a traversal, replace the selected value at node i with probability 1/i. Each node then has final probability 1/n. A stored array of node values instead offers O(1) sampling after O(n) preprocessing and storage. Test repeated values and a single-node list.

Source: Linked List Random Node on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

["Solution","getRandom","getRandom"]
[[[4,9,9]],[],[]]

Output

[null,9,4]

Explanation

This is one possible sample sequence. Value 9 has probability 2/3 because two of the three nodes contain it; 4 has probability 1/3.

Constraints

1 <= node count <= 10^4

-10^4 <= Node.val <= 10^4

At most 10^4 getRandom calls.

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