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710. Random Pick with Blacklist

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Description

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. 1 <= N <= 1000000000
2. 0 <= B.length < min(100000, N)
3. [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.

Solutions

Python3

Java

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