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题目描述

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.

例子

例子 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.`

• What if the linked list is extremely large and its length is unknown to you?
• Could you solve this efficiently without using extra space?

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 `10^4` calls will be made to `getRandom`.

解题思路

• 时间复杂度: `O(n)`
• 空间复杂度: `O(n)`