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382. Linked List Random Node

Topics

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, 10^4].
  • -10^4 <= Node.val <= 10^4
  • At most 10^4 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?