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();
Solution：
思路：
Time Complexity: O(N) Space Complexity: O(N)
Solution Code：
public class Solution {
ListNode head;
Random random;
public Solution(ListNode h) {
head = h;
random = new Random();
}
public int getRandom() {
ListNode c = head;
int r = c.val;
for(int i=1;c.next != null;i++){
c = c.next;
if(random.nextInt(i + 1) == i) r = c.val;
}
return r;
}
}
