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 <= 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.

Github: code.dennyzhang.com

Credits To: leetcode.com

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

- Solution:

**General Thinkings:**

**Key Observations:**

**Walk Through Testdata**

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