# Leetcode: Random Pick with Blacklist

Random Pick with Blacklist

Similar Problems:

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:
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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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

• Solution: XXX

General Thinkings:

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Key Observations:

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Walk Through Testdata

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```// Blog link: https://code.dennyzhang.com/random-pick-with-blacklist

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