Linked List Random Node LeetCode solution in C++

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/**
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 * Definition for singly-linked list.
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 * struct ListNode {
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 * int val;
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 * ListNode *next;
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 * ListNode() : val(0), next(nullptr) {}
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 * ListNode(int x) : val(x), next(nullptr) {}
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 * ListNode(int x, ListNode *next) : val(x), next(next) {}
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 * };
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 */
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class Solution {
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 public:
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  vector<int> v;
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  Solution(ListNode *head) {
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    while (head != NULL) {
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      v.push_back(head->val);
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      head = head->next;
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    }
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  }
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  int getRandom() {
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    return v[rand() % v.size()];
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  }
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};
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/**
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 * Your Solution object will be instantiated and called as such:
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 * Solution* obj = new Solution(head);
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 * int param_1 = obj->getRandom();
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 */