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:
// 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.# class ListNode:# def __init__(self, x):# self.val = x# self.next = Noneimport randomclass Solution:def __init__(self, head):"""@param head The linked list‘s head.Note that the head is guaranteed to be not null, so it contains at least one node.:type head: ListNode"""self.head = headself.length = 0node = headwhile node:self.length += 1node = node.nextdef getRandom(self):"""Returns a random node‘s value.:rtype: int"""idx = random.randint(0, self.length - 1)node = self.headwhile idx:idx -= 1node = node.nextreturn node.val# Your Solution object will be instantiated and called as such:# obj = Solution(head)# param_1 = obj.getRandom()
