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();
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */public class Solution {public ListNode head;public Random rand; /** @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) { this.head = head; } /** Returns a random node's value. */ public int getRandom() { ListNode node = head; int res = head.val; for (int i = 1; node.next != null; i++) { node = node.next; if(sample(0, i) == i) res = node.val; } return res; } public int sample(int min, int max){ return min + (int)(Math.random() * (1 + (max - min))); }}/** * Your Solution object will be instantiated and called as such: * Solution obj = new Solution(head); * int param_1 = obj.getRandom(); */新闻热点
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