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();
class Solution {
public:
/** @param head The linked list's head.
Note that the head is guaranteed to be not null, so it contains at least one node. */
Solution(ListNode* head):cur(head) {
} /** Returns a random node's value. */
int getRandom() {
int val=cur->val;
ListNode *temp=cur;
for(int i=;temp!=nullptr;temp=temp->next,++i)
{
uniform_int_distribution<unsigned> u(,i);
default_random_engine e(rand());//真正随机的种子
unsigned int m=u(e);
if(m<)
{
val=temp->val;
}
}
return val;
}
private:
ListNode *cur;
};