{ "data": { "question": { "questionId": "894", "questionFrontendId": "710", "categoryTitle": "Algorithms", "boundTopicId": 1861, "title": "Random Pick with Blacklist", "titleSlug": "random-pick-with-blacklist", "content": "
You are given an integer n
and an array of unique integers blacklist
. Design an algorithm to pick a random integer in the range [0, n - 1]
that is not in blacklist
. Any integer that is in the mentioned range and not in blacklist
should be equally likely to be returned.
Optimize your algorithm such that it minimizes the number of calls to the built-in random function of your language.
\n\nImplement the Solution
class:
Solution(int n, int[] blacklist)
Initializes the object with the integer n
and the blacklisted integers blacklist
.int pick()
Returns a random integer in the range [0, n - 1]
and not in blacklist
.\n
Example 1:
\n\n\nInput\n["Solution", "pick", "pick", "pick", "pick", "pick", "pick", "pick"]\n[[7, [2, 3, 5]], [], [], [], [], [], [], []]\nOutput\n[null, 0, 4, 1, 6, 1, 0, 4]\n\nExplanation\nSolution solution = new Solution(7, [2, 3, 5]);\nsolution.pick(); // return 0, any integer from [0,1,4,6] should be ok. Note that for every call of pick,\n // 0, 1, 4, and 6 must be equally likely to be returned (i.e., with probability 1/4).\nsolution.pick(); // return 4\nsolution.pick(); // return 1\nsolution.pick(); // return 6\nsolution.pick(); // return 1\nsolution.pick(); // return 0\nsolution.pick(); // return 4\n\n\n
\n
Constraints:
\n\n1 <= n <= 109
0 <= blacklist.length <= min(105, n - 1)
0 <= blacklist[i] < n
blacklist
are unique.2 * 104
calls will be made to pick
.给定一个整数 n
和一个 无重复 黑名单整数数组 blacklist
。设计一种算法,从 [0, n - 1]
范围内的任意整数中选取一个 未加入 黑名单 blacklist
的整数。任何在上述范围内且不在黑名单 blacklist
中的整数都应该有 同等的可能性 被返回。
优化你的算法,使它最小化调用语言 内置 随机函数的次数。
\n\n实现 Solution
类:
Solution(int n, int[] blacklist)
初始化整数 n
和被加入黑名单 blacklist
的整数int pick()
返回一个范围为 [0, n - 1]
且不在黑名单 blacklist
中的随机整数\n\n
示例 1:
\n\n\n输入\n[\"Solution\", \"pick\", \"pick\", \"pick\", \"pick\", \"pick\", \"pick\", \"pick\"]\n[[7, [2, 3, 5]], [], [], [], [], [], [], []]\n输出\n[null, 0, 4, 1, 6, 1, 0, 4]\n\n解释\nSolution solution = new Solution(7, [2, 3, 5]);\nsolution.pick(); // 返回0,任何[0,1,4,6]的整数都可以。注意,对于每一个pick的调用,\n // 0、1、4和6的返回概率必须相等(即概率为1/4)。\nsolution.pick(); // 返回 4\nsolution.pick(); // 返回 1\nsolution.pick(); // 返回 6\nsolution.pick(); // 返回 1\nsolution.pick(); // 返回 0\nsolution.pick(); // 返回 4\n\n\n
\n\n
提示:
\n\n1 <= n <= 109
0 <= blacklist.length <= min(105, n - 1)
0 <= blacklist[i] < n
blacklist
中所有值都 不同pick
最多被调用 2 * 104
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