LeetCode - Linked List Random Node
Question Definition
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();
Java Solution
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
List<Integer> list;
/** @param head The linked list's head.
Note that the head is guaranteed to be not null, so it contains at least one node. */
public Solution(ListNode head) {
list = new LinkedList<>();
while(head != null) {
list.add(head.val);
head = head.next;
}
}
/** Returns a random node's value. */
public int getRandom() {
Random r = new Random();
return list.get(r.nextInt(list.size()));
}
}
/**
* Your Solution object will be instantiated and called as such:
* Solution obj = new Solution(head);
* int param_1 = obj.getRandom();
*/