528. Random Pick with Weight

-
https://leetcode.com/problems/random-pick-with-weight/

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight.
Note:
  1. 1 <= w.length <= 10000
  2. 1 <= w[i] <= 10^5
  3. pickIndex will be called at most 10000 times.
Example 1:
Input: 
["Solution","pickIndex"]
[[[1]],[]]
Output: [null,0]
Example 2:
Input: 
["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
[[[1,3]],[],[],[],[],[]]
Output: [null,0,1,1,1,0]
Explanation of Input Syntax:
The input is two lists: the subroutines called and their arguments. Solution's constructor has one argument, the array w. pickIndex has no arguments. Arguments are always wrapped with a list, even if there aren't any.
---
Related problems
380-insert-delete-getrandom-o1
Intuition
---