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:

1 2 3 4 5 6 7 8

// 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. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ classSolution { private: ListNode* head = nullptr; 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) { this->head = head; }

/** Returns a random node's value. */ intgetRandom(){ auto result = head->val; auto cur = head->next; int i = 2;

while(cur != nullptr) { if(rand() % i == 0) { result = cur->val; } i++; cur = cur->next; }

return result; } };

/** * Your Solution object will be instantiated and called as such: * Solution* obj = new Solution(head); * int param_1 = obj->getRandom(); */