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710. Random Pick with Blacklist
Given a blacklist B containing unique integers from [0, N), write a function to return a uniform random integer from [0, N) which is NOT in B.
Optimize it such that it minimizes the call to system’s Math.random().
Note:
1 <= N <= 1000000000
0 <= B.length < min(100000, N)
[0, N) does NOT include N. See interval notation.
Example 1:
Input:
["Solution","pick","pick","pick"]
[[1,[]],[],[],[]]
Output: [null,0,0,0]
Example 2:
Input:
["Solution","pick","pick","pick"]
[[2,[]],[],[],[]]
Output: [null,1,1,1]
Example 3:
Input:
["Solution","pick","pick","pick"]
[[3,[1]],[],[],[]]
Output: [null,0,0,2]
Example 4:
Input: ["Solution","pick","pick","pick"] [[4,[2]],[],[],[]] Output: [null,1,3,1]
Explanation of Input Syntax:
The input is two lists: the subroutines called and their arguments. Solution's constructor has two arguments, N and the blacklist B. pick has no arguments. Arguments are always wrapped with a list, even if there aren't any.
思路
将黑名单里的数字一一对应到未使用的数字上，如果随机到了黑名单里的数字，返回对应的数字。
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