Description
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 head of the singly-linked list head.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 chosen.
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, 104].
-104 <= Node.val <= 104- At most
104 calls will be made to getRandom.
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?
Solutions
Solution 1
PythonJavaC++Go
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def __init__(self, head: Optional[ListNode]):
self.head = head
def getRandom(self) -> int:
n = ans = 0
head = self.head
while head:
n += 1
x = random.randint(1, n)
if n == x:
ans = head.val
head = head.next
return ans
# Your Solution object will be instantiated and called as such:
# obj = Solution(head)
# param_1 = obj.getRandom()(code-box)
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
private ListNode head;
private Random random = new Random();
public Solution(ListNode head) {
this.head = head;
}
public int getRandom() {
int ans = 0, n = 0;
for (ListNode node = head; node != null; node = node.next) {
++n;
int x = 1 + random.nextInt(n);
if (n == x) {
ans = node.val;
}
}
return ans;
}
}
/**
* Your Solution object will be instantiated and called as such:
* Solution obj = new Solution(head);
* int param_1 = obj.getRandom();
*/(code-box)
/**
* 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:
ListNode* head;
Solution(ListNode* head) {
this->head = head;
}
int getRandom() {
int n = 0, ans = 0;
for (ListNode* node = head; node != nullptr; node = node->next) {
n += 1;
int x = 1 + rand() % n;
if (n == x) ans = node->val;
}
return ans;
}
};
/**
* Your Solution object will be instantiated and called as such:
* Solution* obj = new Solution(head);
* int param_1 = obj->getRandom();
*/(code-box)
/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
type Solution struct {
head *ListNode
}
func Constructor(head *ListNode) Solution {
return Solution{head}
}
func (this *Solution) GetRandom() int {
n, ans := 0, 0
for node := this.head; node != nil; node = node.Next {
n++
x := 1 + rand.Intn(n)
if n == x {
ans = node.Val
}
}
return ans
}
/**
* Your Solution object will be instantiated and called as such:
* obj := Constructor(head);
* param_1 := obj.GetRandom();
*/(code-box)
