linkedListRandomNode.cpp

// Source: https://leetcode.com/problems/linked-list-random-node/
// Author: Miao Zhang
// Date:   2021-02-06

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
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) {
        while (head) {
            nodes_.push_back(head->val);
            head = head->next;
        }
    }
    
    /** Returns a random node's value. */
    int getRandom() {
        return nodes_[random() % nodes_.size()];
    }
private:
    vector<int> nodes_;
};

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