Package g0501_0600.s0528_random_pick_with_weight

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    528 - Random Pick with Weight.

    Medium

    You are given a 0-indexed array of positive integers w where w[i] describes the weight of the <code>i<sup>th</sup></code> index.

    You need to implement the function pickIndex(), which randomly picks an index in the range [0, w.length - 1] ( inclusive ) and returns it. The probability of picking an index i is w[i] / sum(w).

    • For example, if w = [1, 3], the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e., 25%), and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e., 75%).

    Example 1:

    Input "Solution","pickIndex" [[1],[]]

    Output: null,0

    Explanation:

    Solution solution = new Solution([1]);
solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.

    Example 2:

    Input

    ["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
[[[1,3]],[],[],[],[],[]]

    Output: null,1,1,1,1,0

    Explanation:

    Solution solution = new Solution([1, 3]);
solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4.
solution.pickIndex(); // return 1
solution.pickIndex(); // return 1
solution.pickIndex(); // return 1
solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4.

Since this is a randomization problem, multiple answers are allowed.
All of the following outputs can be considered correct:
[null,1,1,1,1,0]
[null,1,1,1,1,1]
[null,1,1,1,0,0]
[null,1,1,1,0,1]
[null,1,0,1,0,0]
......
and so on.

    Constraints:

    • <code>1 <= w.length <= 10<sup>4</sup></code>

    • <code>1 <= wi<= 10<sup>5</sup></code>

    • pickIndex will be called at most <code>10<sup>4</sup></code> times.