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().


  1. 1 <= N <= 1000000000
  2. 0 <= B.length < min(100000, N)
  3. [0, N) does NOT include N. See interval notation.

Example 1:

Output: [null,0,0,0]

Example 2:

Output: [null,1,1,1]

Example 3:

Output: [null,0,0,2]

Example 4:

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

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

  • Solution: XXX

General Thinkings:

Key Observations:

Walk Through Testdata

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


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