Linked List Random Node
Problem Statement - link #
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.
Implement the Solution class:
Solution(ListNode head)Initializes the object with the integer array nums.int getRandom()Chooses a node randomly from the list and returns its value. All the nodes of the list should be equally likely to be choosen.
Examples #
Example 1:
Input
["Solution", "getRandom", "getRandom", "getRandom", "getRandom", "getRandom"]
[[[1, 2, 3]], [], [], [], [], []]
Output
[null, 1, 3, 2, 2, 3]
Explanation
Solution solution = new Solution([1, 2, 3]);
solution.getRandom(); // return 1
solution.getRandom(); // return 3
solution.getRandom(); // return 2
solution.getRandom(); // return 2
solution.getRandom(); // return 3
// getRandom() should return either 1, 2, or 3 randomly. Each element should have equal probability of returning.
Constraints #
- The number of nodes in the linked list will be in the range
[1, 10^4] -10^4 <= Node.val <= 10^4- At most
10^4calls will be made to getRandom.
Solutions #
/**
* 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:
//Note : head is guaranteed to be not null, so it contains at least one node.
ListNode* HeadNode;
Solution(ListNode* head) {
HeadNode = head;
}
//returns value of a random node
int getRandom() {
int res, len = 1;
ListNode* x = HeadNode;
while(x){
if(rand() % len == 0){
res = x->val;
}
len++;
x = x->next;
}
return res;
}
};
/**
* Your Solution object will be instantiated and called as such:
* Solution* obj = new Solution(head);
* int param_1 = obj->getRandom();
*/